The Constitutional Court of Korea declared in the decision of 2021 HunMa975 on March 23, 2023 that the unconstitutionality of Articles 46(2) and 57(1) and (2) of the Family Relationship Registration Act for infringing upon the constitutional right to be registered at birth for illegitimate children born to married women, ordering the legislature to enact remedial legislation by May 31, 2025. This paper proposes a scientific method for determining paternity, whereby a biological father can prove paternity through a test conducted by an agency certified by the Minister of Justice before the child’s birth. In such cases, the presumption of paternity can be immediately rebutted, allowing the biological father to register the child as his own. The paper also suggests that after the child’s birth as a child of his mother’s husband, a biological father can bring an action to deny of paternity in condition that he can demonstrate that his wife could not have conceived a child with her husband due to a long-term separation at the time of conception and if he becomes aware of this fact within two years of the child’s birth. This proposal seeks to strike a balance between the principles of bloodline truth and the child’s welfare.