Anak dari perkawinan yang tidak dicatatkan berakibat anaknya tidak mempunyai hubungan perdata terhadap ayah biologisnya. Keberadaan Putusan Mahkamah Konstitusi Nomor 46/PUU-VIII/2010 mengubah hubungan keperdataan anak luar kawin terhadap ayah biologisnya. Dimata KHI dan UU 1/1974 terdapat perbedaan pengaturan mengenai anak luar kawin, sehingga dalam penerapannya pun berbeda. Tesis ini membahas mengenai efektifitas putusan Mahkamah Konstitusi terhadap KHI dan UU 1/1974, serta akibat dari putusan itu dalam hal terjadinya pewarisan khususnya anak luar kawin terhadap ayah biologisnya. Penelitian ini menggunakan metode yuridis normatif yang diuraikan secara deskriptif. Hasil penelitian ini menyimpulkan bahwa putusan Mahkamah Konstitusi tersebut menyimpang dari ketentuan mengenai anak luar kawin dalam KHI dan UU 1/1974, sehingga akibatnya dalam hal pewarisan, putusan tersebut tidak wajib diikuti selama bertentangan dengan ajaran agama.

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The children who are born on unregistered marriage do not have a civil relationship with their biological father. The existence of Constitutional Court Decision Number 46/PUU-VIII/2010 has changed the civil relationship of children who born out of wedlock with their biological father. There are differences between the compilation of Islamic Law and Marriage Law Number 1 of 1974 on regulatory and enforcement regarding children born out of wedlock. The thesis discussed about the effectiveness of Constitutional Court Decision Number 46/PUU-VIII/2010 against the compilation of Islamic Law and Marriage Law Number 1 of 1974, including the consequences of the decision toward the right of children born out of wedlock to inherit from their father. The thesis concluded that Constitutional Court Decision Number 46/PUU-VIII/2010 has deviated from the compilation of Islamic Law and Marriage Law Number 1 of 1974 on children born out of wedlock regulation thus the decision is not compulsory to be adhered as long as it is contrary to the religion.