Section 781(1) of the Korean Civil Code was amended on March 31, 2005 to provide that: (1) A child shall assume her or his father’s surname and origin of surname. But in a case of the child whose parents agreed to follow its mother’s surname when they got married, the child shall assume her or his mother’s surname and the origin of surname. A new subsection, §781(6), was enacted to provide, in relevant part, that: “the court may permit a child’s original surname and origin of surname to change when her or his surname need to be changed for the child’s welfare. (the rest omitted)” This Article explores the application, the implications, and the elements of the child’s welfare in the petition for change of the child’s surname, with analytical studies on the cases filed in the family court, Gwang-Ju district court. It first starts with the decision of the Constitutional Court holding patronymy unconstitutional. Part Ⅱ argues the several necessities of change of child’s surname suc