Marriage of one clan is a marriage carried out by the same clan and marriage is prohibited because it is still considered one blood or siblings in traditional Batak karo. The purpose of this study was to determine the development of restrictions on single tribe marriage that occurred in the Yogyakarta region. The method used in this study is normative research, with a focus on the facts of legal norms and social norms. The results of this study are that the development of one marga's marriage is getting better and is rarely done because the indigenous Karo Batak people still respect customary rules. The conclusion of this study is that overseas factors do not affect community adherence to customary law. The suggestion of this research is for the indigenous people of Batak Karo to continue to publish the rules for prohibiting the marriage of traditional Karo Batak to be maintained and there are no indigenous Batak Karo people who violate customary rules.