Abstract: Objective To observe effects of low level lead diet on cellular immune function in mice.Methods Mice were randomly divided into six groups.They received different level lead diets for eight weeks.Serum TNF-αlevel and lymphocyte subsets were measured.The pathological and ultra structural changes of spleen were determined.Results Low level lead diet resulted in a decreased number of CD₄ T-cell.But significant difference was found in CD₈ T-cell among all groups(P<0.05).Serum TNF-αin the lowest level was significantly increased;but other groups were lower than control group.The splenic coefficients of all trial groups significantly decreased compared with the control group.Conclusion The low level of lead diet,even at relative low level of lead diet could impaire cell-mediated immunity and be harmful to the spleen and thymus.In spite of no other overt clinical disorder,immune function was impaired.