According to Article 7 paragraph (1) of the Compilation of Islamic Law marriage for people who are married according to Islamic law can only be proved by the Deed of Marriage made by the Registrar Officer. On one hand, the marriage law states that marriage registration is the only evidence of the occurrence of marriage, but the law provides way out for people who cannot prove the existence of such marriage by way of determination of marriage (itsbat nikah) from the Religious Courts. This research aim at to elaborate the cours of sirri marriage and procedures of re- establishment (itsbat) of marriage at the religious court of Bantul. It is a normative and empirical legal research. The result of this research shows that (Itsbat nikah) is a re-establishment of marriage that has been done, because of doubt on whether or not the marriage is legitimate, or the marriage cannot be proven by authentic deed (marriage certificate). The applicant appealed to the Religious Courts, so that the marriage can be legalized, and to further obtain the marriage certificate. Itsbat nikah is one of the authority of the Religious court. The existence of itsbat from the Religious Court will affect the marital status, where the marriage has been have the power of the law, the children who are born in the marriage received state recognition, and provide a guarantee on the rights of wives and children.