Abstract: Objective To avert the effect of various doses of selenium on lead-induced placenta of preg nant rats.Methods SD rats were randomly divided into 5 groups.From GD1 to GD20,the lead-poisoning group rats were fed 2mg/ml lead acetate solution by drinking.The selenium-rivalry group rats were fed 2,4,8μg/ml sodium-selenite solution by drinking on the base.The control group rats drink double evapor ate water randomly.In GD250,the blood lead and selenium of pregnant rats were detected by atomabsor ption spectrum,and the serum alkaline phosphates by AMP balanced solution.T he alkaline phosphates of placenta were detected by immunohistochemisty technique.The morpholo gical changes of placenta were observed by the transmission election microscope and microscope.Results The level of blood lead and ALP had no sing ificant difference between MA group and the control group was very similar.There was no significant difference in the content of the blood selenium among all groups(P<0.05).Conclusion 4 μg/ml sodium-selenite can provide significant protective effects on the hazards of the 2 mg/ml lead acetate in SD pregnant rats placenta.The selenium's elig ible addition in pregnancy can improve the placental function obviously.