Can An Illegitimate Child Use His Father’s Last Name?

Published on December 22, 2022

Last name for an illegitimate child

In the Philippines, an illegitimate child is assigned his or her mother’s last name while the middle name field is left blank. The child should not be given the mother’s middle name because then it would appear that they are siblings. This could potentially cause problems in their important transactions such as when the child gets a passport or enrolls in school.

An illegitimate child may carry his or her father’s last name by virtue of RA 9255 or the Act Allowing Illegitimate Children to Use the Surname of their Father. This, however, will largely depend on the child’s birthdate and year, as well as the father’s cooperation and willingness to have his child carry his last name.

Republic Act 9255

This Act provides a blueprint for the assignment of last names for illegitimate children. Under RA 9255, all illegitimate children born on or after March 19, 2004 may use their father’s last name provided that an Authority to Use the Surname of the Father (AUSF) and the father acknowledges the child as his are executed.

How does a father acknowledge his illegitimate child?

How to acknowledge an illegitimate child

A father must expressly acknowledge an illegitimate child as his by executing any of the following instruments:

  • Affidavit of Admission of Paternity (AAP) found at the back of the child’s Certificate of Live Birth (COLB).
  • Affidavit of Acknowledgment as provided under Memorandum Circular 04-12 of the Office of the Civil Registrar General
  • Private Handwritten Instrument (PHI) – handwritten and signed by the father stating that he recognizes the child as his for the rest of his life.

How to file the admission of paternity:

  • The father, mother, or the child himself (if already of legal age) may file the Affidavit of Admission of Paternity and Affidavit to Use the Surname of the Father (AUSF) at the Local Civil Registry Office where the child’s birth certificate was registered.
  • If the proof of paternity is a PHI, the father must personally file this at the LCRO.
  • If the father is deceased but left a PHI, this can be filed by the mother or the child himself if he is already of legal age.
  • The LCR shall review the submitted documents as well as the entries in the COLB. If all entries are deemed correct and accurate, these will be recorded in the Register of Legal Instruments.
  • The child’s COLB shall be annotated on the Remarks portion of the Register of Births. Take note that child’s new last name shall not be placed on the last name field of the birth certificate, rather, it will appear as an annotation.
  • The annotated COLB as well as certified copies of the admission of paternity (AAP, Affidavit of Acknowledgment, or PHI) shall be issued.

Does the filing of the AUSF and admission of paternity include the assignment of a middle name for the child?


A Supplemental Report must be filed to supply the child’s middle name. Include the documents used for the admission of paternity as well as the AUSF when submitting the supplemental report at the LCR.

Can RA 9255 be used even if the father did not expressly acknowledge the child?


The AUSF and admission of paternity documents are non-negotiable requirements. Without these, the child’s last name cannot be changed to his or her father’s.

Other reminders:

Getting an illegitimate child’s last name changed to his or her father’s by virtue of RA 9255 does not make the child a legitimate child. It simply allows the child to use his or her father’s last name publicly (IDs, passport, documents, etc.).

For an illegitimate child to become legitimate, his or her parents must marry and file for a legitimation. Upon legitimation, the child receives the right to use his or her father’s last name.

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