Chlorpyrifos (CPF) is used intensively as an insecticide. There is a high risk of interference with the aquatic environment due to unconscious use and has a negative effects especially fish. In this study, the responses of rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta fario) exposed to the same pollutants have been evaluated and compared in terms of target organs. Fish were exposed to different concentrations of CPF (0.25, 0.5, and 1 mu g L-1) through 21 days. After the process oxidative stress [superoxide dismutase (SOD), catalase (CAT glucose-6-phosphate dehydrogenase (G6PD), glutathione reductase (GR), glutathione-S-transferase (GST), glutathione peroxidase (GPx)], acetylcholinesterase (AChE) and malondialdehyde (MDA) have been measured in gill, kidney and liver tissues. CPF exposure led to a significant changes in the enzyme activities and decreased AChE in all tissues (p<0.05). All antioxidant enzyme activities and MDA levels showed tissue-specific alterations (p<0.05). These results put forward a close relationship between AChE inhibition and chlorpyrifos concentrations. In addition to, CPF concentrations caused oxidative stress and inhibition in all enzyme activities of two different trout species' gill, liver and kidney tissues.