In a sale and purchase whose object of value is usually a contract or sale and purchase agreement for smooth transactions and also to make it easier for sellers and buyers if in the future there is something that can harm the parties. An agreement is an event where one person promises to another person or where two people promise each other to do something. In this thesis research the author will examine the default committed by the buyer for not paying properly even though the seller has carried out his obligations, namely sending shrimp feed. This research uses normative legal research, uses legal principles approach and case approach, and qualitative techniques. Default can also be intended as the implementation of obligations that are not timely or carried out improperly. The form of default by the defendant (buyer) in the cooperation agreement to purchase shrimp feed in Decision Number 1056/Pdt.G/2019/PN Jkt. Brt, is included in the category of carrying out what has been promised, but not as promised. The process of settling the default case in the Cooperation Agreement for the Purchase of Shrimp Feed in Decision Number 1056/Pdt.G/2019/PN Jkt. Brt has complied with the applicable regulations and the author also agrees with the judge's decision in this case.