Abstract: The experiment was conducted to examine the effect of dietary high molybdenum(Mo) on the antioxidant′s function of liver and spleen in broilers. 300 one-day-old avian broilers were randomly divided into four groups, and fed on diets as follows: control diet (Mo 13 mg·kg^-1) and high molybdenum diets(Mo 500 mg·kg^-1, high molybdenum group Ⅰ; Mo 1 000 mg·kg^-1, high molybdenum groupⅡ; Mo 1 500 mg·kg^-1, high molybdenum group Ⅲ) for 6 weeks. The superoxide dismutase (SOD), glutathion peroxidase (GSH-Px) and xanthine oxidase (XOD) activities were lower (P<0.01) and the malondialdehyde（MDA）contents were higher(P<0.01) in liver and spleen in high Mo groups Ⅱand Ⅲ than that in control group. Changes of the above mentioned enzymes activities and MDA contents in serum were consistent with those of liver and spleen. Pathologically, hepatocytes in high Mo groups showed granular degeneration and vacuolar degeneration. The statistical analyses by FCM indicated that the G0/G1 phase was increased (P<0.01) and the G2+M phase, S phase and the PI (Proliferating index) were decreased (P<0.01) of spleen in high molybdenum groups Ⅱ and Ⅲ. The results showed that dietary molybdenum in excess of 1 000 mg·kg-1 impaired antioxidant′s function in liver and spleen, inhibit the development of the spleen.