Marriage agreement constitutes deal between future husband and wife to stipulate the marriage consequences on their property wealth that is distorted from property unity. In the Article 147 of Civil Law and Article 29 of Law No.1 of 1974 about Marriage was stipulated on legal action of marriage agreement composition, that is performed before or when marriage was held. If husband and wife do not make the agreement of marriage yet, that both of them have a job where their job has high risk of the reduction up to end of their capital asset that have been gotten, in order to make their future life and the education of their children, it is important to make the marriage agreement after the marriage done by the principle of the State Court Establishment. The approach method used in this research is normative juridicial, that is, research that look on its legal effective in the middle of people. This approach method used in order to know the application of law decision in Civil Code and laws of marriage also the rule of its execution in relation with the practice on the field. In practice, there was marriage agreement composition that performed by both husband-wife couple, after marriage was held by propose on State Court to make decree upon it. This legal action was not stipulated either within Civil Law regulation and or marriage law. This issue raise problems in the administration process of the marriage deed and impacted toward the third parties. This research was aimed to know the judge’s foundations and considerations when decide those proposal and its legal consequence after the establishment from state court. Based on result, it may conclude that judge’s foundations and considerations to grant the marriage agreement proposal after the marriage was the agreement of both parties, husband and wife, the existence of their dereliction and unknowing about stipulation of marriage agreement that must be arranged before the marriage, and the existence of jurisprudence from previous stipulation. This attained because State Court as the respected legal institution, which its legal products must be obeyed by everybody. Legal consequence agreement is tied both parties, namely husband and wife. Its legal consequence upon property wealth position became separate one each other, while upon the third parties, it has tied power, as long as the third parties were not feel inflicted by such stipulation. / Perjanjian kawin merupakan persetujuan antara calon suami dan calon istri untuk mengatur akibat perkawinan terhadap harta kekayaan mereka yang menyimpang dari persatuan harta kekayaan. Pasal 147 Kitab Undang-Undang Hukum Perdata dan Pasal 29 Undang-Undang Nomor 1 Tahun 1974 tentang Perkawinan mengatur perbuatan hukum pembuatan perjanjian kawin yang dilakukan sebelum atau pada saat perkawinan dilangsungkan. Apabila ada suami-istri belum membuat perjanjian kawin dan keduanya bekerja dimana tempat mereka bekerja mempunyai resiko akan habisnya harta kekayaan yang diperoleh, maka demi masa depan kehidupan dan pendidikan anak-anak mereka diperlukan perjanjian kawin setelah perkawinan dilangsungkan dengan dasar Penetapan Pengadilan Negeri. Penelitian ini dilakukan dengan metode pendekatan yuridis normatif, yaitu penelitian yang melihat efektifitas hukum dalam masyarakat. Metode pendekatan ini digunakan untuk mengetahui penerapan ketentuan hukum dalam Kitab Undangundang Hukum Perdata dan Undang-undang Nomor 1 Tahun 1974 Tentang Perkawinan serta peraturan pelaksanaannya dalam kaitannya dengan praktek di lapangan. Pada prakteknya terdapat pembuatan perjanjian kawin oleh pasangan suamiistri sesudah perkawinan berlangsung dengan mengajukan permohonan Penetapan Pengadilan Negeri. Hal ini tidak diatur dalam Kitab Undang-Undang Hukum Perdata dan Undang-Undang Perkawinan sehingga menimbulkan berbagai persoalan dalam proses pencatatan dalam akta perkawinan serta akibatnya bagi pihak ketiga. Penelitian ini bertujuan untuk mengetahui dasar dan pertimbangan Hakim memutus permohonan penetapan tersebut serta akibat hukumnya terhadap pihak ketiga setelah adanya Penetapan Pengadilan Negeri. Hasil penelitian ini menyimpulkan bahwa dasar dan pertimbangan hakim mengabulkan permohonan pembuatan perjanjian kawin setelah perkawinan dilangsungkan adalah adanya persetujuan suami-istri, adanya kealpaan dan ketidaktahuan mereka tentang pembuatan perjanjian kawin sebelum perkawinan, dan adanya yurisprudensi dari penetapan sebelumnya. Perjanjian kawin itu harus dibuat dengan akta Notaris. Akibat hukum pembuatan perjanjian kawin setelah perkawinan tersebut adalah mengikat suami-istri tersebut, akibat hukum terhadap kedudukan harta menjadi terpisah satu dengan yang lain, sedangkan untuk pihak ketiga mempunyai kekuatan mengikat selama pihak ketiga tersebut tidak merasa dirugikan.