This study was carried out in a domestic, slaughter house and industrial discharging region of Ceyhan River and under the crest of the Aslantas Dam on the same river. In this study, the state of water quality and their effects on some hematological parameters of African Catfish (Clarias gariepinus) was identified. Reserach, in the area under the crest of the Aslantas Dam (station I) located on the Ceyhan River and discharging region on the same river (station II). water temperature, chemical oxygen demand (COD), pH, nitrate (NO3-N), nitrite (NO2-N), ammonia (NH3-N) and soluble reactive phosphorus (SRP) values were determined in these two stations. The study was realised on 45 fish from each station during the summer seasons (June, July, August). The hematological parameters included erythrocyte (RBC) and RBC indices (MCV: mean corpuscular volume, MCH: mean corpuscular hemoglobin, MCHC: mean corpuscular hemoglobin consentration), leukocyte (WBC), haemoglobine (Hb), hematocrit (Hct) values and leukocyte cell formulas (lymphocyte, monocyte, neutrophil, eosinophil), serum glucose and protein levels were evaluated. The physico-chemical parameters observed that the water at station II had higher COD, NH3-N, NO2-N, pH and SRP than at station I. In this study, WBC values and leukocyte cell formulas of C. gariepinus were found increasing by means of environmental stressors and also, RBC, RBC indices, Hb and Hct values were determined decreasing in C. gariepinus collected from station II (p<0.05). On the other hand, serum glucose levels were increased and protein levels were decreased in station II. The study was found to be important in the biomonitoring of pollution of aquatic ecosystems, in terms of rational use of hematological parameters.