Tender conspiracy is one of the anti-competition act prohibited under Article 22 of Law No. 5 Year 1999 on Prohibition of Monopolistic Practices and Unfair Business Competition. The practice of tender conspiracy in Indonesia has dominated the total cases of business competition handled by KPPU, totaling approximately seventy percent. As one of the violations which is almost always injurious, the tender conspiracy is only regulated by a rule of reason approach that gives room of interpretation of the consequences of the violation. Tender conspiracy was also proven to be conducted by the reported parties in the case that had been decided by KPPU in the KPPU Decision Number: 06/KPPU-L/2015. The questions that arise in connection with the rampant practices of tender conspiracy is how are they regulated in the applicable law, and how does KPPU decide on the practice of tender conspiracy in the case concerned in accordance with the law. The aim is to examine the causes of the rampant practice of tender conspiracy in relation to the regulations governing it, as well as to review the KPPU's decision on real tender conspiracy case. For this reason, author uses normative research with qualitative analysis techniques on secondary data, and uses the statute approach and case approaches. The results of the study indicate that the law that regulates tender conspiracy is not yet clear and often leads to multi-interpretation. KPPU as the business competition supervisory authority has not provided a calculation of sanctions that is in accordance with the applicable KPPU Regulations. In addition, the approach used in the law is not effective, and KPPU should conduct its supervisory function not only after the violation has occurred but before so as to prevent the occurrence of violations.