Sinapine is a natural compound occuring generally in Cruciferae and its radioprotective effects on germinating seeds of wheat and barley has been identified. Experimental results showed that sinapine had no toxicity to mice. The 6 weeks old mice were either fed with sinapine at 24 h before irradiation or continued feeding for 30 d after irradiation. The condition of irradiation was that all of the animals were exposed to 5.8Gy whole body X-radiation. The results of irradiation showed that sinapine could assuage the severe decreases of white blood cell and platelet counts in peripheral blood, but had no significant effects on the contents of hemoglobin. Feeding with sinapine during 30d after irradiation could significantly promote the recovery of platelet counts in mice.