In this study, effects of sublethal concentrations of fenbutatin oxide on catalase (CAT) and superoxide dismutase (SOD) activities and lipid peroxidation in muscle, liver, kidney and brain tissues of Cyprinus carpio were investigated. The 96-hours LC50 value for fenbutatin oxide was determined as 1.544 mg/L for C. carpio in this study. 0.15 mg/L (1/10 of LC50) and 0.30 mg/L (1/5 of LC50) sublethal concentrations were applied for 96 h (4 days) in this experiment. The CAT activities in tissues were increased relation to doses applied. The SOD activities were decreased by 0.30 mg/L. The tissue MDA levels were significantly increased in relation to dose applied.