Abstract: The experiment was conducted to study the effect of copper toxicity on blood findings in chickens. 180 one-day-old Avian broilers were divided into three groups, and fed on diets as follow: （1）control (Cu 11.92 mg/kg)，（2）copper toxic I (Cu 650 mg/kg) and （3）copper toxic Ⅱ ( Cu 850 mg/kg) for six weeks. The signs began to appear at the 2nd week in copper toxic group Ⅱ and at the 3rd week in copper toxic group I. Some of affected chickens died during the experiment. Hematopathologically, red cells in toxic groups I and II became deformed. The populations of red cells, hemoglobin contents and serum caeruloplasmin activity were much lower, and the serum copper concentrations, activities of lactate dehydrogenase and glutamicoxaloacetic transaminase were much higher in copper toxic groups than in control group. Mechanism of copper toxicity on blood findings is also discussed .