Abstract: Objective To explore nicotinamide' antagonising immunosuppression action induced by UV.Methods We used monoclonal antibody immunifaction,neutral red colorimetric analysis,MTT method to measure the number of langerhans cells(LC),phago cytosis of macrophage in abdominal cavity and multiply function of spleen T cell.Intensity of Delayed Type Hy persensitivity (DTH)was measured with sliding caliper by us.Results In positive control group intensity of DTH was restrained.The number of LC in the ear and back of the mice and the multiply function of spleen T cell were lower than the purely induced group and nicotinamide group(P<0.01).The nicotinamide group appeared DTH and the number of LC in the ear and back,phagocytosis of macrophage in abdomical cavity,the multiply function of spleen T cell were higher than the positive control.Conclusion Nicotinamide can antagonize immunosuppression action induced by UV.