ABSTRAKPasal 43 Undang-Undang Nomor 1 Tahun 1974 tentang Perkawinan menyebutkan, “anak yang dilahirkan di luar perkawinan hanya mempunyai hubungan perdatadengan ibu dan keluarga ibunya.” Artinya pasal ini menerangkan bahwa segala hal yang terkait dengan hak anak yang lahir di luar perkawinan hanya dibebankankepada ibunya, sedangkan ayah biologisnya tidak dibebankan untuk memenuhi hak anak tersebut. Dalam perkembangannya, berdasarkan Putusan MahkamahKonstitusi Nomor 46/PUU-VIII/2010, anak di luar perkawinan memiliki hubungan perdata dengan ibu dan keluarga ibu, serta ayah dan keluarga ayah biologisnyaselama dapat dibuktikan adanya hubungan darah di antara mereka. Hal ini bertolak belakang dengan hukum Islam yang mengatur bahwa anak zina hanyamemiliki hubungan perdata dengan ibu dan keluarga ibunya saja. Muncul pertanyaan apakah yang menjadi dasar pertimbangan Mahkamah Konstitusi menetapkan hubungan perdata anak di luar perkawinan dengan ayah biologisnya, dan bagaimana akibat hukum dari Putusan Mahkamah Konstitusi terhadap nasab anak di luar perkawinan, serta tinjauan teori hifzhu nasl terkait Putusan Mahkamah Konsitusi tersebut. Penelitian ini menggunakan metode yuridis normatif dengan jenis penelitian kepustakaan. Hasil penelitian ditemukan bahwa Putusan Mahkamah Konstitusi menimbulkan makna yang ambigu, karena tidak ada definisi yang jelas terkait frasa “anak di luar perkawinan.” Menurut teori hifzhu nasl menasabkan anak di luar perkawinan (anak zina) kepada ayah biologisnya merupakan suatu tindakan yang akan merusak eksistensi dari maqᾱṣidal-syar’iyyah. Namun jika yang dimaksud adalah anak yang lahir dari “pernikahan di bawah tangan,” maka hal ini sesuai dengan ketentuan maqᾱṣid al-syar’iyyah.Kata kunci: anak di luar perkawinan, hubungan perdata, hifzhu nasl. ABSTRACTIn Article 43 of Law Number 1 of 1974 on Marriage, it is stated that, “a child born out of wedlock has nothing more than a legal relation to the mother and her family.” To be precise, this article defines that a mother is fully responsible for all matters concerningthe rights of her child born out of wedlock, whereas the biological father is not charged to fulfill the rights of the child. In its progression, based on the Constitutional Court’s Decision Number 46/PUU-VIII/2010, the child born out of wedlock has a legal relation to his mother and the family, and also an illegitimacy to his putative father and the family, as long as it is proven there is a lineal consanguinity (blood tie) between them. This isinconsistent with the Islamic law which stipulates that an illegitimate child has only a legal relation to his mother and the family. The arising questions pertain on the basis of consideration of the Constitutional Court in determining the illegitimacy of a child born out of wedlock to his putative father, and the implication of Constitutional Court decisions to the consanguinity of a child born out of wedlock, as well as the theory of “hifzhu nasl” responding to the decision of the Constitutional Court. This analysis is a literature-basedresearch conducted using a juridical normative method. The results of the analysis arrive at a conclusion that the Constitutional Court’s decision is significantly ambiguous, as regards there is no clear definition of the associated phrase of “child born out of wedlock.”According to the theory “hifzhu nasl,” the settling on the consanguinity of a child out of wedlock (illegitimate child) to the putative father would undermine the prevailing concept of maqᾱṣid al-syar’iyyah. But if the concern is about the child born of “underhandedmarriage”, then it conforms to the provisions of maqᾱṣid al-syar’iyyah.Keywords: child born out of wedlock, legal relation, hifzhu nasl.