Business competition in the business world is already a natural thing for business people. But, there are deviant businesses who are dishonest, hinder other businesses, etc. Therefore, the Government has enacted Law No. 5 of 1999 on Prohibition of Monopolistic Practices and Unfair Business Competition to prevent and minimize unfair competition in businesses. The author conducts research on cases of unfair business competition at PT. Tirta Investama. This case began with the case of PT. Tirta Fresindo Jaya against PT. Tirta Investama. Indeed, KPPU has done an investigation this case. Based on KPPU's decision No. 22/KPPU-I/2016 PT. Tirta Investama and PT. Balina Agung Perkasa committed a violation of an exclusive dealing as stipulated in article 15 paragraph 3 letter b and market control contained in article 19 letter a and b of Law No. 5 of 1999 on Prohibition of Monopolistic Practices and Unfair Competition and imposed a sanctions of Rp 20.13 billion. In this case study, the author also conducted a research on the mechanism for handling business competition cases by KPPU against PT. Tirta Investama. This research is a normative legal research/ library research and uses qualitative descriptive data analysis. This approach uses a case approach. In this case using two approaches, namely per se illegal and rule of reason. The law, this law is based on how the law must be applied, and KPPU has been appropriate in handling this case based on various considerations, legal facts and applicable provisions.