This study aimed to determine the effect of agency cost on the performance of firms listed in the Kompas100 index on the Indonesia stock exchange for the 2016-2021 period. In determining the sample, this research applied the purposive sampling method. This study used a sample of 46 companies and managed a total of 248 observations. The findings indicated a negative and significant impact of agency cost on firm performance. Companies with a high agency cost tend to reduce the performance. Mitigating these adverse effects requires the implementation of robust internal controls, transparent reporting mechanisms, and effective corporate governance practices.