BACKGROUND: Atrazine is one of the most important and effective pollutants in aquatic ecosystems. The widest sugar cane farms of the Middle East are located in Khouzestan province, Iran. Large amounts of Atrezine are being used in farming on these farms.                  Objectives: The aims of this study were to investigate acute toxicity (LC50 96 h) of atrazine on Barbus grypus and the effects of chronic toxicity with sub-lethal concentration of atrazine on hematological parameters as well. Methods: 180 B grypus were divided into 4 equal groups (5, 10 and 20% of LC50 96 h and control). Blood samples were taken on days 0, 7, 14 and 21 of experiment. Hematological parameters including hemoglobin level, hematocrit, and red blood cells (RBC), white blood cells (WBC), and globular indices were measured and compared among the groups. Results: LC50 96 h was measured 65 mg l-1. Hematological parameters were  significantly affected by chronic toxicity of atrazine. Hemoglobin, hematocrit and RBC were decreased at all sampling periods in fish exposed to different levels of atrazine (p<0.05). There were no significant changes in globular indice values among the groups in sampling periods (p>0.05). For all samples, WBC value was decreased significantly on day 21 (p<0.05). Conclusions: Based on the results, it can be concluded that chronic atrazine toxicity adversely affects hematological parameters of B. grypus.