In the present study, antioxidant enzymes activity and lipid peroxidation level during oxidative stress in rainbow trout during exposure to Diazinon and effect of vitamin E, Selenium and C on the reduction of its adverse effects were investigated. In this study, sixty rainbow trout fish with the average weight of 121±18 g [±SD] were allocated into four treatment groups: control Diazinon (0.1 mg L 1) vitamin C (300 mg kg 1 in diet) plus Diazinon (0.1 mg L-1) and vitamin E Selenium (vitamin E 100 mg kg 1 in diet + Se 0. 5 mg kg 1 in diet )plus Diazinon (0.1 mg L-1).Then at the end of the second and fourth week of fish blood serum samples to measure enzyme super oxide dismutase (SOD), Catalase (CAT), total antioxidant level (TAC) and malondialdehyde index (MDA) was performed. According to the findings, SOD activity in the fish treated with Diazinon (without vitamin) was significantly (P<0.05) lower than the control group, but the group of vitamins C and E selenium were maintained at the level of controls. Also, the enzyme activity of CAT in groups of Diazinon (without of vitamin), vitamin C and vitamin E selenium increased significantly (P<0.05) compared to the control group, but this increase in vitamin E selenium had less difference with the control group. The total antioxidant capacity in vitamin E selenium and Diazinon (without of vitamin) groups had the highest and lowest levels, respectively. On the other hand, MDA levels in Diazinon (Without of vitamin) group was higher than other groups, whereas in vitamin E selenium and C groups there was no significant difference observed from the control group. Results showed that supplementation of vitamin E selenium and C act both as anti-oxidation in the process of oxygen free radicals removal caused by Diazinon metabolites. However, the ability of anti-oxidation vitamin E selenium is higher than vitamin C. Overall, the use of vitamin supplements mentioned in rainbow trout diets to increase antioxidant defenses and reduce oxidative damage during organophosphate poisoning seems effective.