The main objective of this study is to determine the effects of some hematological and blood biochemical parameters of nitrite concentrations on Oreochromis niloticus. Fish were exposed to acute nitrite (0.1, 1.0 and 5.0 mg/L) at 24 hours and 96 hours, respectively. Blood samples from fish were analyzed in order to identify and evaluate changes in the hematological parameters (Hct, Hb, RBC and WBC), some plasma biochemical parameters (cortisol, glucose and cholinesterase) and reduced glutathione (GSH). Autoanalyser spectrophotometric methods were used in determining all blood parameters. When compared to control fish, the most increase in hematological parameters was found in Hct and WBCs (66 % and 25 %) of all nitrite concentrations at 24 hours and 96 hours, but Hb and RBCs decreased by 53 % and 15 % in all concentrations. Blood biochemical parameters, compared to control fish, except for cholinesterase, it was observed that cortisol and glucose levels were increased in exposure medium and time. Cortisol levels were increased in 5.0 mg/L nitrite (approximately 3 hold) and glucose levels were increased in 28 % at 24 hours and 96 hours. However, cholinesterase levels of fish blood decreased this concentration. Nitrite exposures did not alter GSH levels in the blood, but its levels decreased in the 1.0 mg/L nitrite exposed to fish. In our study, blood parameters indicated that O. niloticus were sensitive to the distribution of nitrite on aquatic systems.