The aim of the present study is to investigate the oxidative stress index in Capoeta capoeta treated with carbaryl and 2,4-dichlorophenoxyacetic acid (2,4-D). Fifty Capoeta capoeta fish caught in Kars Creek were equally divided into five groups and acclimatized in separate tanks for 10 days. The fish were kept in tanks as follows: Group I (control) was kept in normal water. Group II, III, IV and V were kept in separate tanks containing 0.3 mg/L carbaryl, 0.6 mg/L carbaryl, 10 mg/L 2,4-D and 20 mg/L 2,4-D, respectively. The blood and liver samples were taken from the fish for biochemical studies at the end of the study period. Oxidative stress index (OSI) in plasma were evaluated as well as AST and ALT levels in the liver. Plasma OSI and liver AST levels in the groups with carbaryl and 2,4-D were compared with the control group, and they were found to be significantly higher. As a result, it was concluded that carbaryl and 2,4-D administered under of LC₅₀ value caused liver damage by increasing the oxidative stress of Capoeta capoeta.