I. Overview

In the Philippines, a child’s surname is not merely a matter of preference; it is governed by statutes, administrative rules, and jurisprudence that reflect the child’s status (legitimate or illegitimate), the existence and form of recognition by the father, and the applicable procedures for recording civil status events.

As a general rule, an illegitimate child uses the mother’s surname. An illegitimate child may use the father’s surname only under conditions set by law and implementing regulations, primarily when paternity is acknowledged/recognized in the manner required by the Civil Code, the Family Code, and civil registry rules.

This guide explains the legal bases, the recognized modes of acknowledgment, the documentary and procedural requirements, and the practical outcomes and limitations of using the father’s surname.

II. Key Legal Framework

A. Family Code and the General Rule on Surnames of Illegitimate Children

Under Philippine family law, illegitimate children are generally under the mother’s parental authority, and in the ordinary course, they bear the mother’s surname. The law, however, allows an illegitimate child to bear the father’s surname when the father has recognized the child in a legally acceptable manner.

B. Republic Act No. 9255: The Statutory Gateway

Republic Act No. 9255 amended the Family Code provisions on illegitimate children so that they may use the surname of their father if:

Paternity is acknowledged by the father (through specific documentary means); and
Proper civil registry recording is made, following implementing rules.

RA 9255 is the central statute used today for the administrative process of changing/recording the illegitimate child’s surname to the father’s surname in the civil registry.

C. Implementing Rules and Civil Registry Procedures

The day-to-day application of RA 9255 is carried out through civil registry rules (Philippine Statistics Authority and Local Civil Registry Offices) that prescribe the Affidavit of Acknowledgment / Admission of Paternity, the Public Instrument requirement, and the Affidavit to Use the Surname of the Father (AUSF), among others.

The AUSF procedure is administrative (civil registry-based). It is distinct from court actions such as petitions to correct entries, legitimate/illegitimate status suits, or actions involving contested paternity.

III. Definitions and Concepts You Must Understand

A. Illegitimate Child

A child is illegitimate if conceived and born outside a valid marriage, subject to certain legal classifications and exceptions. Illegitimate status affects (1) the child’s surname rules, (2) parental authority, and (3) inheritance rights (discussed briefly below).

B. Recognition / Acknowledgment of Paternity

For an illegitimate child to use the father’s surname, the father must recognize or acknowledge the child in a legally acceptable form. Recognition is not simply verbal; it must be expressed through written instruments or civil registry entries as required by law and regulations.

C. Use of Father’s Surname vs. Legitimation

Allowing an illegitimate child to use the father’s surname does not automatically make the child legitimate. Legitimation (which may occur when parents who could have married at the time of conception subsequently marry, subject to legal conditions) changes status. RA 9255/AUSF primarily affects surname usage and the record of recognition, but not the child’s legitimacy status by itself.

IV. When an Illegitimate Child May Use the Father’s Surname

The illegitimate child may use the father’s surname if paternity is acknowledged by the father in any of the recognized modes, and the civil registry is properly updated.

A. If the Father’s Name Is on the Birth Certificate AND He Signed It

If the father personally appears and signs the Certificate of Live Birth (COLB) or the acknowledgment portion in accordance with civil registry rules, that is typically treated as a form of acknowledgment.

Practical consequence: With the appropriate documentary setup, the child can be recorded to use the father’s surname, often through AUSF processing or through proper initial registration (depending on timing and local registry practice).

B. If the Father Executes an Affidavit of Acknowledgment / Admission of Paternity

If the father signs an affidavit admitting paternity—often titled Affidavit of Acknowledgment or Affidavit of Admission of Paternity—this constitutes recognition.

This affidavit generally must be:

Notarized, and
Executed in proper form to be acceptable to the Local Civil Registry Office (LCRO) and/or PSA.

C. If the Father Recognizes the Child Through a “Public Instrument”

A “public instrument” generally refers to a notarized document (or a document that by law is treated as a public document) where the father acknowledges the child.

Examples can include:

Notarized deeds or sworn statements expressly acknowledging paternity
Certain notarized agreements that explicitly state recognition of the child

D. If the Father Recognizes the Child in a Private Handwritten Instrument

Recognition may also be done in a private handwritten instrument, subject to proof of authenticity and compliance with implementing rules.

However, in practice, civil registry acceptance often depends on:

Clear expression of recognition,
Proper identification of the child, and
Evidence that the instrument is genuinely executed by the father (and not forged).

Because private instruments can be disputed more easily, administrative registrars may scrutinize them more closely and may require supporting documentation.

V. The AUSF: What It Is and What It Does

A. What “AUSF” Means

AUSF stands for Affidavit to Use the Surname of the Father. It is the sworn document and administrative mechanism used to have an illegitimate child’s civil registry record reflect the use of the father’s surname, provided that the father has legally acknowledged the child.

B. Legal Effect of AUSF

AUSF results in:

Recording that the child is using the father’s surname; and
Annotating or updating relevant civil registry entries following the prescribed process.

Critically, AUSF:

Does not by itself change legitimacy status.
Does not automatically alter inheritance classification (though recognition can have implications, the illegitimate status remains unless legitimation/adoption applies).
Does not confer parental authority to the father by surname change alone (parental authority rules remain governed by the Family Code and related jurisprudence; the mother generally retains parental authority over an illegitimate child, absent special circumstances).

VI. Who May File or Execute the AUSF

Depending on the child’s age and the applicable implementing rules in practice:

A. The Mother (As Parent/Guardian)

Often, the mother is the one who files with the LCRO, particularly when the child is a minor, to reflect the use of the father’s surname, provided the father has executed the recognition document.

B. The Father

The father’s participation is primarily through acknowledgment of paternity (signature on birth certificate or affidavit/public instrument). In some settings, the father may also participate in filing or supporting documentation, especially if registration is being completed contemporaneously.

C. The Child (If of Age)

For children who are already of age, civil registry practice may require or allow the adult child to initiate or join the application, depending on the registry’s procedural requirements.

Because civil registry procedures can be sensitive to age and consent rules, the safest approach is to ensure the registrable facts (acknowledgment) are properly documented and then align the filing with local registry requirements.

VII. Core Requirements in Practice (Documentary Checklist)

Although exact documentary lists can vary by LCRO practice, AUSF processing commonly requires:

PSA/LCRO Copy of the Certificate of Live Birth (or certified true copy from the LCRO where registered).
Proof of Paternity Acknowledgment, such as:
- Birth certificate where the father is indicated and he signed appropriately; or
- Affidavit of Acknowledgment/Admission of Paternity; or
- A qualifying public instrument; or
- A qualifying private handwritten instrument (with proof/authentication requirements).
Affidavit to Use the Surname of the Father (AUSF), properly accomplished and notarized.
Valid IDs of affiants (mother/father, and sometimes the child if of age).
Marriage documents only if relevant to legitimation issues (not required for AUSF alone unless the registry asks for context).
Supporting records (as needed) such as baptismal certificate, school records, or other identity documents—typically used when there are discrepancies or late registration contexts.

VIII. Where to File: LCRO and PSA Workflows

A. Local Civil Registry Office (LCRO)

AUSF is typically filed at the LCRO where the child’s birth was registered (or where the record is kept under local procedure). The LCRO evaluates the documents, records the appropriate annotation, and transmits updates per civil registry protocols.

B. Philippine Statistics Authority (PSA)

After LCRO action and transmission, the updated/annotated record becomes available through PSA issuance processes. Timelines vary depending on transmission and processing.

IX. Common Scenarios and How the Rules Apply

Scenario 1: Father Did Not Sign the Birth Certificate, But Wants the Child to Use His Surname

Solution: The father executes an Affidavit of Acknowledgment/Admission of Paternity (or another acceptable instrument), then the AUSF is filed and processed through the LCRO.

Scenario 2: Father’s Name Appears on the Birth Certificate, But There Is No Proper Acknowledgment/Signature

If the father’s name appears without proper acknowledgment, the LCRO may treat the entry as insufficient for RA 9255 purposes. The remedy is usually to submit the father’s formal acknowledgment instrument and proceed with AUSF (or correct the registry entry if required).

Scenario 3: Father Is Abroad

A father abroad can acknowledge paternity by executing the necessary sworn instrument before:

A Philippine embassy/consulate (consularization), or
A foreign notary/public authority, typically with authentication/apostille processes as applicable, then submitted for civil registry acceptance.

Scenario 4: Father Is Deceased

If the father did not acknowledge the child while alive in a legally acceptable way, using his surname via AUSF becomes difficult. In such situations, remedies may shift to:

Establishing filiation through evidence and potentially judicial action (depending on facts, especially if contested), rather than purely administrative AUSF.

Scenario 5: Father Denies Paternity

AUSF is not a tool to force paternity acknowledgment. If paternity is disputed, the matter may require court determination of filiation, supported by evidence. Administrative AUSF hinges on acknowledgment; it is not meant to adjudicate contested parentage.

X. Limitations and Legal Consequences of Using the Father’s Surname

A. It Does Not Legitimize the Child

Using the father’s surname under RA 9255 does not transform an illegitimate child into a legitimate one. Legitimation requires separate legal requisites.

B. Parental Authority Generally Remains with the Mother

For an illegitimate child, parental authority is generally with the mother. The father’s acknowledgment and surname usage may be relevant in obligations (e.g., support), but surname usage alone does not automatically alter custody/authority rules.

C. Support and Other Obligations

Recognition of paternity may strengthen enforceability of the father’s obligations, particularly support, because paternity is expressly acknowledged in a formal way. However, support issues are still determined by law, facts, and enforceable processes.

D. Inheritance Rights Remain Based on Status

Illegitimate children have inheritance rights, but the shares and rules differ from those for legitimate children. Using the father’s surname does not by itself rewrite succession rules; the child remains illegitimate unless status changes via legitimation or adoption.

XI. Relationship to Legitimation and Adoption

A. Legitimation

Legitimation may apply when the parents were not married at the time of the child’s conception/birth but could have been legally married at that time (i.e., no legal impediment), and later do marry. If legitimation occurs, the child’s status changes, and the surname and civil registry entries may be updated accordingly through the appropriate processes.

B. Adoption

Adoption is a separate legal pathway that can change a child’s status and name according to the adoption decree and rules. It is not interchangeable with AUSF.

XII. Practical Drafting Notes for AUSF and Acknowledgment Instruments

A. Clarity of Identity

Documents should clearly state:

Child’s full name (as registered)
Date and place of birth
Mother’s name
Father’s name
Clear statement that the father recognizes the child as his

B. Consistency Across Records

Inconsistencies in spelling, middle names, or birth details can trigger delays. When inconsistencies exist, registrars may require:

Additional identity documents, or
Separate correction processes.

C. Notarization and Proper Execution

Because recognition often relies on notarized instruments, ensure:

Proper notarial acknowledgment
Valid identification of affiants
Compliance with notarial rules (especially for overseas execution)

XIII. When Court Action May Be Necessary Instead of AUSF

AUSF is designed for administrative recording where recognition is not in genuine dispute. Court proceedings may be needed when:

Paternity is contested and must be adjudicated.
There are serious defects in civil registry records that require judicial correction rather than administrative annotation.
The father is deceased without prior valid recognition and the child seeks to establish filiation against the estate or for other legal reasons requiring adjudication.
There are competing claims or fraud allegations involving civil registry entries.

XIV. Evidence and Proof Issues in Establishing Filiation

Even outside AUSF, Philippine law recognizes that filiation may be proven by:

Civil registry records
Open and continuous possession of status as a child
Other admissible evidence (depending on the nature of the proceeding)

However, AUSF is not an evidentiary trial mechanism; it relies primarily on formal acknowledgment instruments and registry compliance.

XV. Common Pitfalls and How to Avoid Them

Assuming the father’s name on the birth certificate is enough If the father did not properly acknowledge/sign, the entry may not qualify. Obtain proper acknowledgment documentation.
Using informal letters or messages Social media messages and casual letters are generally not the kind of “instrument” contemplated for recognition in civil registry processes. Use notarized affidavits or acceptable instruments.
Ignoring name inconsistencies Align spellings and identifiers; address discrepancies through proper correction processes if needed.
Treating AUSF as legitimation AUSF is surname-use; legitimation requires separate legal requisites and processes.
Proceeding administratively when paternity is disputed Disputed paternity usually requires judicial intervention.

XVI. Summary of the Step-by-Step Administrative Route (Typical)

Secure proof of paternity acknowledgment (birth certificate signature or father’s notarized acknowledgment instrument).
Prepare and notarize the AUSF with the proper affiant(s) and details.
File with the LCRO where the birth is registered (or as local procedure allows).
Comply with LCRO evaluation and any additional documentary requirements.
Wait for annotation/transmittal so that the record is updated.
Request the updated/annotated PSA birth certificate once processing is reflected.

XVII. Core Takeaways

The default rule is: illegitimate child uses the mother’s surname.
The exception route is RA 9255: an illegitimate child may use the father’s surname if the father acknowledges paternity through legally recognized documentation and the change is properly recorded/annotated via AUSF and civil registry procedures.
AUSF affects surname usage and registry entries; it does not automatically change legitimacy status, parental authority rules, or inheritance classification.
If paternity is contested or recognition is not available, judicial remedies may be necessary.