Here’s a comprehensive, practice-oriented legal explainer for the Philippine setting. I’m not using search, so treat this as expert guidance you can use to brief counsel or to prepare filings—but always confirm current implementing rules and fee schedules with the Local Civil Registrar (LCR) and the Philippine Statistics Authority (PSA). This is general information, not legal advice.

Change of Surname of an Illegitimate Child in the Civil Registry (Philippines)

1) Baseline rule: surname of the mother

Under the Family Code (Art. 176, as later amended), a child born outside wedlock (i.e., illegitimate) uses the mother’s surname by default.
The mother also exercises sole parental authority over the child unless a court orders otherwise.

2) How an illegitimate child may use the father’s surname

There are three main legal pathways seen in practice. Each has different paperwork, venues, and effects:

A. Administrative route under the “use of father’s surname” framework (no court case)

When available: The father admits paternity through the forms/documents recognized by civil registration rules (e.g., at or after birth).

Core ideas:

You typically file an Affidavit to Use the Surname of the Father (AUSF) with the LCR where the birth was recorded (or via “out-of-town” filing with your current LCR for forwarding).
The AUSF must be supported by proof of paternal acknowledgment, commonly one or more of:
- Affidavit of Admission of Paternity (AAP) executed by the father;
- The father’s signature on the Certificate of Live Birth acknowledging paternity; or
- A private handwritten instrument signed by the father expressly acknowledging the child.

Who signs the AUSF?

If the child is 18 or over: the child signs/executes the AUSF in their own behalf.
If the child is a minor: the mother ordinarily files/signs the AUSF on behalf of the child (some LCRs also require the child’s written consent once of discernment age; check local practice).

Where it’s filed and what happens:

File at the LCR; pay documentary/annotation fees.
The LCR annotates the child’s birth record to reflect the use of the father’s surname and forwards the annotation to PSA for issuance of a PSA-certified copy with annotation.

Key cautions:

This route does not confer legitimacy and does not transfer parental authority to the father.
It establishes surname use grounded on acknowledged filiation for civil-registry purposes; rights to support from the father follow the Family Code, but legitimacy remains unchanged.

B. Judicial route to establish filiation and correct the record (Rule 108 + evidence)

When used: The father did not sign any admission document, refuses to cooperate, is unavailable, or the LCR rejects an administrative filing due to insufficient acknowledgment.

Mechanics in brief:

File a Rule 108 petition (cancellation/correction of entries in the civil registry) before the Regional Trial Court with jurisdiction over the LCR or the child’s residence.
Make it a properly adversarial proceeding (implead civil registrar, father, and all interested parties; publish as required).
Seek: (i) judicial declaration of filiation based on proof (e.g., credible documentary/ testimonial evidence; DNA when available), and (ii) directive to annotate the birth record so the child may use the father’s surname.
Upon final judgment, present the entry of judgment to the LCR/PSA for annotation and issuance of a PSA copy.

Effect: Child remains illegitimate (unless another law applies), but surname may be changed to the father’s by court-ordered annotation.

C. Status-changing routes that incidentally change the surname

These are not mere “use of surname” cases—they transform the child’s legal status, and surname change follows as a consequence:

Legitimation by subsequent marriage of the parents (Family Code, as amended):
- If parents marry each other after the child’s birth and no legal impediment existed between them at conception, the child becomes legitimate by legitimation.
- LCR processes legitimation and annotates the birth record; the child assumes the father’s surname as a legitimate child.
Adoption (now largely administrative under the latest adoption regime):
- Adoption creates legitimate filiation with the adopter(s).
- The NACC/LCR issues or causes issuance of a new/annotated birth record reflecting the adoptive father’s (or parents’) surname.

⚠️ RA 9048/10172 notes: Administrative correction laws let you fix clerical errors, first name/nickname, day/month of birth, and sex (when clerical). They do not generally authorize surname change of an illegitimate child unless you are within the specialized frameworks above (AUSF/acknowledgment, legitimation, adoption, or a Rule 108 court order).

3) Documents and typical LCR requirements (administrative AUSF track)

Exact checklists vary by LCR, but expect some combination of:

Accomplished AUSF (child, if 18+; otherwise mother on child’s behalf)
Proof of paternal acknowledgment: AAP, father-signed COLB, or handwritten admission by the father
Valid IDs of the affiant(s) and, if required, father’s ID
PSA or LCR copy of the birth certificate (to be annotated)
Parents’ CENOMAR/marriage certificate, if relevant to assess legitimation route or conflicts
Passport/IDs of the child (if any), for cross-reference of name usage
Fees (annotation, documentary stamps, certification, expedited/express if applicable)

Where filed:

Original LCR of registration; or current LCR (out-of-town filing) which relays to the LCR of record; PSA receives the endorsement for national records.

Turnaround:

Annotation at LCR can be relatively quick; PSA issuance of the annotated record can take longer. Time these steps before school enrollment, passport, or travel.

4) Effects and non-effects of using the father’s surname

What changes:

The child’s surname on the civil registry and, after annotation, on government IDs, school records, passports (upon application to update).
The civil registry now records acknowledged filiation to the father for naming purposes.

What does NOT change:

Legitimacy: The child remains illegitimate unless later legitimated/adopted.
Parental authority: Still with the mother unless a court orders otherwise.
Custody: Not automatically altered.
Succession rules: Filiation matters for support and inheritance, but the rules differ from those of legitimate children; the surname itself doesn’t equal legitimacy.

5) When the father is deceased, unreachable, or uncooperative

No administrative path works without admission/acknowledgment traceable to the father.
If there is no AAP/COLB signature/handwritten admission, the usual remedy is judicial:
- File Rule 108 to correct the civil registry (pair it with a cause of action to establish filiation).
- Present best available evidence (e.g., DNA, authentic communications, financial support records, photos, testimony).
- If the court finds filiation, it may order the surname change and direct the civil registrar/PSA to annotate the record.

6) Conflicts, objections, and special cases

Existing surname usage in school/IDs: After annotation, you’ll need to harmonize records (school, PhilSys, passport, bank). Keep certified copies of the annotated PSA birth certificate for re-issuance or correction of downstream records.
Child’s preference (teens and above): Even when the mother may file, many LCRs will seek the child’s written consent as a matter of prudence. Courts also consider best interests of the child.
Multiple admissions or contested paternity: If more than one man claims paternity or there’s an objection, expect the LCR to deny administrative action and refer to court.
Mother married to someone else: Presumptions of legitimacy arise that complicate status; consult counsel—this may require impugning legitimacy within strict prescriptive periods, not an AUSF.
Religious/foreign-law issues: These do not override Philippine civil registry rules for entries recorded in the Philippines.

7) Reverting or further changing the surname

If the child adopted the father’s surname via AUSF and later disagrees, options depend on age and circumstances:
- If still a minor, the mother may petition (administratively or judicially) citing best interests; contested cases may require Rule 108.
- If of age, the person can seek judicial change of name (Rule 103) or a Rule 108 correction, showing proper and reasonable cause (e.g., long, consistent use; protection/welfare concerns).
Upon legitimation/adoption, the surname will follow the new status and the latest court/administrative order.

8) Downstream updates after successful annotation

PSA: Secure multiple PSA-certified copies showing the annotation.
School & PRC/CHED/DepEd: File name-change/record-update requests.
PhilSys (National ID), LTO, SSS/GSIS, PhilHealth, Pag-IBIG: Update membership records.
Passport: Apply for a new passport reflecting the annotated surname (bring old passport, PSA copy, IDs).
Banking/Insurance: Update KYC records to avoid mismatches.

9) Practical timelines, fees, and tips

Plan ahead—PSA reissuance with annotation can take weeks; courts take months.
Bring originals and photocopies; some LCRs require 2–3 sets.
Keep official receipts and control numbers.
For court cases, anticipate publication costs (Rule 108), process service, and attorney’s fees.
If the child needs the surname for imminent travel or school, consider interim certifications from the LCR while waiting for the PSA copy.

10) Quick decision guide

Do you have a father’s AAP/COLB signature/handwritten admission? Yes → File AUSF at LCR → Annotation → Update records. No → Consider Rule 108 (with filiation proof) → Court order → Annotation.
Parents later married each other and no impediment existed at conception? Yes → Legitimation process at LCR → Child becomes legitimate and uses father’s surname.
Child being adopted? Yes → Follow adoption process → New/annotated record with adopter’s surname.

11) Common misconceptions—cleared up

“Using the father’s surname makes the child legitimate.” ❌ False. It does not. Only legitimation or adoption changes status.
“Once the father’s surname is used, custody shifts.” ❌ False. Mother retains parental authority unless a court rules otherwise.
“RA 9048 lets us change the child’s surname at the LCR anytime.” ❌ Generally no. Surname changes for illegitimate children proceed under AUSF/acknowledgment, legitimation, adoption, or Rule 108 court order.

12) What to prepare for counsel or the LCR

Current PSA/LCR birth certificate
Any acknowledgment documents (AAP, COLB signed by father, handwritten admission)
Valid IDs (mother/child/father as needed)
Proofs of filiation (photos, communications, remittances, DNA if available) for judicial route
Marriage certificate (if legitimation route fits) or adoption papers (if applicable)

If you want, tell me your province/city LCR, the child’s age, and what acknowledgment papers you have (if any). I can draft a step-by-step filing plan and a document checklist tailored to your route—administrative AUSF vs. Rule 108 vs. legitimation/adoption.