In Indonesia, legal land ownership has law protection, but in fact land ownership often recognized by people who do not own the land. This often occurs due to several things, which is wanting to take over in an unlawful manner, such as falsifying land documents, and others. Because of this, the writer interested in exploring more deeply about illegal occupancy of land in this final paper. In this final project, the writer has formulated 3 problem. First, how Wihelmina Tai control the land in terms of Law No. 5 of 1960 concerning Basic Agrarian Principles. Second, how land occupation by the defendant based on the Basic Agrarian Law number 5 of 1960 concerning Basic Agrarian principles and Law 51 of 1960 concerning the Prohibition Use of Land Without an Eligible Permit or Authority. Third, how is the legal certainty of land ownership by Wilhemina Tai, in illegal occupancy of land dispute based on the Atambua District Court decision No. 09 / PDT.G / 2015 / PN.Atb. In this paper the writer used normative legal research method. With this method the writer can analyze deeper because this research method is based on the existing rules so it becomes a foundation for writers in providing arguments. Research results from final project based on judicial decisions and regulations in Indonesia that there was an illegal occupancy of land by 4 defendants, The defendant act against the law, and based on the witnesses who have been presented, and evidence such as tax payment letter of the land, it has been proven that the plaintiff is the person who actually owns the disputed land. The plaintiff has owned the disputed land based on the customary inheritance of the plaintiff's mother, and because it has been proven that there is a grave of the plaintiff's family so that the plaintiff won in this case. In addition to this, the plaintiff also had a mistake in this case, namely because the plaintiff had not registered her land.