Cartel is crucial problem in competition law in many countries, including Indonesia. Cartel creates market distortion where the price of goods and services are increasing, higher than the price which is created by fair market. This harmful to consumer. Cartel commonly created in oligopoly markets, which make the new undertakings are difficult to entry the market. Unfortunately, cartel eradication has big issue related to obtain evidences, because of the high confidentiality among cartel members. It makes United States of America and Germany implements leniency program in their competition law. This research is aiming to know: (i) how the leniency program in United States of America Competition Law, Germany Competition Law, and Indonesia Competition Law are regulated dan implemented to eradicate cartel? and (ii) how to regulate and implement leniency program that suit to Indonesia and optimizing the enforcement of Competition Law? This research used normative legal research. Meanwhile, type of data which is used is primary legal materials, secondary legal material, and tertiary legal materials. Then, the data in this research are obtained using literature review method. Researcher using comparative approach and induction analysis. The research results some conclusion, that United States of America and Germany have some similarities and differences. The similarities consist of subject, has their own authority/division, type of leniency, marker system, one door of division to be contacted, some of requirements, revocation of leniency, and confidentiality provision. While, the differences cover: amount of applicant that can get leniency, period of marker, and leniency plus and penalty plus. Implementing leniency program in eradicating cartel will be optimal if it implemented together with whistle blower and indirect evidence. Leniency not only reduce the cost which used by authority to uncover cartel, also enhancing the detection and deterrence effect of creating new cartels in the future because of distrust between the cartel conspirator in advance. This also should support with high detection risk, severe sanction and transparent legal enforcement process.