We studied the protective effect of Echinacea purpurea against radiation by evaluating changes in the peripheral blood cell count and peripheral blood antioxidant activity. Echinacea purpurea administration had a suppressive effect on radiation-induced leukopenia, especially on lymphocytes and monocytes and resulted in a faster recovery of blood cell counts. Mouse peripheral blood antioxidant activity was increased by Echinacea purpurea, and a relationship between the suppressive effect on radiation-induced leukopenia and the antioxidant effect was suggested.