In medieval law of Thailand country. the Ayutthaya period has a biblical Scriptures treatise of Justice as a legal article that came from India which define the criteria. Conduct for the general public, including the king. Thammasat Scriptures have characteristics comparable to constitutional law itself. The King used to create a legal treatise Scriptures and there has been significant improvement of the law, it is the legal instrument is adjusted to samduang, which is a compilation of laws and legal classification of the. The legal instrument that has samduang the law as a legal act, contracts, inheritance, family, criminal. so that in the Ayutthaya period, thammasat has Scriptures and also modified the laws seal samduang.