The agreement for broadcasting commercial advertisements on the radio is proof of an agreement for the smooth broadcasting of products by the radio party in accepting work from the advertiser/advertising agency, but in practice there is still a default from one of the parties even though the agreement made has fulfilled the legal requirements according to Article 1320 of the Civil Code. This article aims to determine the process of forming the agreement and to see the causes of default in the implementation of the commercial advertisement broadcasting agreement carried out on CJDW FM radio, in order to avoid similar problems in the future.The research method used is qualitative with a descriptive case study approach that describes the legislation in Indonesia, namely the Civil Code and Law Number 32 of 2002 concerning Broadcasting, which is then linked to legal theory and its implementation. Based on the results of the research that the contents of the commercial advertisement broadcasting agreement on CJDW FM radio are in accordance with Article 1320 of the Civil Code, although the implementation of some of its contents does not go according to the agreement of the parties, this is known as default, so that after knowing the cause of the problem, efforts can be made to avoid the problem. Similar.