Abstract: Purpose : To observe antiradiation effect of polysaccharides of seaweed (PS) . Methods : After 2 Gy γ-2ray irradiation , the peripheral blood lymphocyte and bone marrow micronuleus test of mice were conducted.Results : The f requency of micronucleus in peripheral blood lymphocyte and bone marrow polychromatoery throcyte increased when the mice were exposed to 2 Gy γ-ray irradiation. Compared with positive cont rol group , the frequency of micronucleus in peripheral blood lymphocyte was markedly decreased by PS(20 mg/ kg·bw and 40mg/ kg·bw) , and the frequency of micronucleus in bone marrow polychromatoerythrocyte was markedly decreased by PS(10 mg/ kg·bw , 20 mg/ kg·bw and 40 mg/ kg·bw) . Conclusion : PS has significant effect of protecting chromosome f rom irradiation injuries。