Insecticides and fertilizers are the most common agrochemicals that enter aquatic ecosystems from farmlands via different ways and consequently affect fish. In this study, effects of dimethoate, and Bacilar, as a bio-fertilizer, on oxidative stress and biochemical parameters were measured in common carp. For this purpose, fish were exposed to 16 and 32 μg L dimethoate, 0.1 and 0.2 ml L Bacilar and the mixtures of both compounds for 14 days. The results showed that Bacilar increased aspartate aminotransferase (AST) and LDH in gills, AST in liver and the activity of catalase (CAT) (0.2 ml L) in kidney, but decreased the activity of lactate dehydrogenase (LDH) and glucose 6-phsphate dehydrogenase (G6PDH) in liver. Dimethoate, alone or in combination with Bacilar, significantly increased LDH, alkaline phosphatase (ALP), AST and CAT activities in gills. Fish exposure to dimethoate, alone or in combination with Bacilar, resulted in a significant decrease in LDH, G6PDH activities, total antioxidant (TA) and glycogen levels in liver and TA in kidney. A significant increase was observed in malondialdehyde (MDA), ALP, AST, alanine aminotransferase (ALT) and CAT activity in liver and kidney of fish exposed to dimethoate alone or in combination with Bacilar. The results showed that cytotoxicity of Bacilar and dimethoate combination depended on their concentrations. Higher concentrations of Bacilar induced significant changes in some biochemical parameters. Dimethoate or/and Bacilar, in sub-lethal concentrations, induced oxidative damages in fish. Finally, these data support the hypothesis that changes in biochemical parameters were induced by exposure to dimethoate and/or Bacilar.