Short answer. Yes, if the father has expressly recognised the child — through the record of birth in the civil register, an admission in a public document, or a private handwritten instrument. Without one of those three acts by the father, the child uses the mother's surname.
What the law says
Illegitimate children shall use the surname and shall be under the parental authority of their mother, and shall be entitled to support in conformity with this Code.
RA 9255, Section 1 — Surname Of Illegitimate Children. Read the full provision →
What the law says
illegitimate children may use the surname of their father if their filiation has been expressly recognized by the father through the record of birth appearing in the civil register, or when an admission in a public document or private handwritten instrument is made by the father
RA 9255, Section 1 — Surname Of Illegitimate Children. Read the full provision →
The default, and the door out of it
The rule opens with the position that applies unless something is done about it: Illegitimate children shall use the surname and shall be under the parental authority of their mother, and shall be entitled to support in conformity with this Code. Then comes the exception this law added, which is what makes the question worth asking at all: illegitimate children may use the surname of their father if their filiation has been expressly recognized by the father through the record of birth appearing in the civil register, or when an admission in a public document or private handwritten instrument is made by the father.
It has to be the father's own act
Every one of the three routes is something the father does — signing the record of birth, making an admission in a public document, or writing one out by hand. A mother cannot supply it, and neither can the father's family, however willing. That is the point most enquiries founder on: an absent or uncooperative father cannot be made to recognise a child by anyone's say-so, and simply writing his surname on a form does not create the recognition the provision requires. Where he will not act, the route is a judicial action to establish filiation, which is a different and heavier proceeding.
May, not shall
Recognition opens a possibility rather than compelling a result. The child may use the father's surname; nothing in the sentence obliges anyone to change a name already in use, and the choice belongs with the child's interests rather than with either parent's preference. Weigh the practical side honestly: school records, identification documents, passports and benefit claims all key off the registered name, and a change made late means a trail of documents in two names to reconcile. Earlier is easier, and consistency across records matters more than which surname is chosen.
The father keeps a way to contest it
The provision closes with a qualification that is easy to miss: Provided, the father has the right to institute an action before the regular courts to prove non-filiation during his lifetime. So recognition is not beyond challenge — the man who made it may go to court to prove that the child is not his, and the right is his alone and expires with him. Note also what recognition does not do. Parental authority stays with the mother under the same sentence, and the surname does not transfer it.