Objective: To investigate the effect of vitamin B12 on the growth and hemopoiesis of broilers. Methods: The Arbor Acres broilers were fed the experimental diets with different doses of vitamin B12 0.00, 0.008, 0.016, 0.024 mg/kg for 3 weeks. The body weight gain and hematologic indices of the broilers were measured. Results: Vitamin B12 deficiency in the diet could depress the body weight gain and feed conversion ratio of the broilers, decrease the amount of red blood cell and hemoglobin, enlarge the volume of red blood cell, increase the content of each cell hemoglobin, reduce platelet in blood. While 0.008 mg/kg vitamin B12 was added in the experimental diets, the body weight gain and feed conversion ratio of the broilers increased markedly. Furthermore, when 0.016mg/kg vitamin B12 was added to the diet, the number of the red blood cell and the content of hemoglobin of the broilers increased significantly, and the shape and volume of the red blood cell became ordinary. There were significants interrelations between BWG,RBC,Hb,PCV,PLT,MCV,MCH of the broilers and the addition of vitamin B12 in the diet. Conclusion: Vitamin B12 deficiency could result in the megaloblastic animia. 0.02-0.03 mg vitamin B12 per kilo diet was required to maintain the growth and normal hemopoiesis of the broilers.