In principle, a child born during the marriage of his or her parents follows his or her biological father's surname and example (Civil Act Article 781, Paragraph 1).

However, in order to resolve problems such as psychological difficulties and inconveniences in social life that children in remarried families experience because their last name is different from that of their stepfather, a system was introduced through the revision of the Civil Act in March 2005 that allows changing a child's last name and surname with permission from the Family Court if necessary for the child's welfare (Article 781, Paragraph 6 of the Civil Act).

A father, mother, or child can file a claim. However, if the child is a minor and a legal representative cannot file a claim, a relative (blood relatives within the 8th degree of consanguinity, in-laws within the 4th degree of consanguinity, and spouse) or a prosecutor may file a claim.

You can file a request with the family court at the address of the child for whom you wish to change your last name.

Simply changing the child's last name does not change the paternity, and the biological father is still listed as the father on the child's family relationship certificate. If you want to terminate the paternity relationship with the biological father and indicate the remarried spouse as the father on the child's family relationship certificate, you must adopt the child as the remarried spouse's biological adoptive child and create a new paternity relationship.