Fenitrothion is being increasingly used as an insecticide under intensive cultivation to control vegetables and fruits pests. The bioconcentration of fenitrothion 2 different groups of freshwater fish (Oreochromis niloticus) was investigated after 28 days of exposure. One tenth of the determined 96 h-LC50 concentrations applied to fish. Fenitrothion concentration was 3.85 mg kg-1 and the Bioconcentration Factors (BCFs) after the experimental period 28 days 675.43 for whole fish body while the concentration was 1.51 mg kg-1 with respective BCFs was reached 264.91 for muscle tissue were 1.61 after daily exposure during the experimental time 28 days. Results concluded that the fenitrothion has ability to fenitrothion bioconcentration factor was high in whole fish compared to muscle tissue.