On March 23, 2023, the Constitutional Court pronounced that ‘the right to be registered immediately after birth of a child’ is a constitutional a fundamental right under the constitution, and ruled that the provisions of the Act on the Registration, Etc. of Family Relationships, which do not include any clause allowing the birth of a child who is born to a married woman and a man other than her husband to be reported by the child’s biological father are nonconforming to the Constitution. This decision has opened the way for children whose births were not registered for the above reasons to be registered according to the improved legislation.
 Meanwhile, on June 22, 2023, shortly after this decision, the Board of Audit and Inspection announced the facts about children who were killed or abandoned without having their births registered. With this as an opportunity, the National Assembly expedited discussions on supplementary legislation. Consequently, a revised ‘Act on the Registration, Etc. of Family Relationships’, which introduces a birth registration system with the addition of a birth notification system in medical institutions, is scheduled to be implemented on July 19, 2024, after being amended on July 18, 2023.
 However, the amended law will not be applied retroactively. Furthermore, even with the implementation of the birth notification system, it will only apply within a limited scope, restricted to Korean nationals. Therefore, the Constitutional Court's decision, still has meaning.
 In this paper, I examined how the right to be registered immediately after birth of a child rooted in international legal norms, can be found as a fundamental right. I also explained its legal nature, specific content, and limitations. Additionally, I also argued about family relationships under the Constitution and examined that the right to report child’s birth of the biological father out of wedlock should be included within the broad scope of constitutional child custody right.