While de minimis rule is mostly applied in Anglo-Saxon law, it has a more limited function in Continental law. On the other hand, the rule is frequently seen in various fields of European Union law, especially the competition law. In the context of competition law, de minimis rule can be defined as considering some agreements, concerted practices and decisions which would be the violation of competition law under normal circumstances as negligible, because their effects on the market are insignificant. While European Union competition law makes detailed regulations about de minimis rule, there has not been a clear regulation regarding the rule in Turkish competition law until recently and the rule was mainly given shaped with the decisions of Turkish Competition Authority. Since the source of the regulation in Turkish law is mainly European Union competition law, it was preferred to handle the subject comparatively. At first, the definition of de minimis rule and its relationship with similar concepts are discussed, then the regulations in European Union competition law are examined. Lastly, the situation in Turkish competition law is studied by dividing the subject into two as before and after the law amendment in 2020.