Many species of Cruciferae are very resistant to ionizing radiation. The inhibition of barley growth induced by X-irradiation was reduced by pre-irradiation treatments with seedling extracts of Brassica napus, B. chinensis or B. juncea. The extracts of seedling of B. napus, B. chinensis, B. juncea, B. juncea var. crispifolia, B. oleracea, Raphanus sativus and the extracts of the infloreseences and leaves of Rorippa montana had the similar effect on wheat. The results showed that the radiation resistance of these cruciferous plants may relate to some natural radiation protective substances in these plants. Sinapine is widely distributed in Cruciferae. The reactions of rape extract in qualitative analysis were identical to those of sinapine. Pre-irradiation treatments of wheat and barley seeds with the solution of sinapine thiocyanate crystals extracted from rape showed similar radiation protective effect. The results of ESR spectra of sinapine-thymine binary systems showed that sinapine protected thymine Many species of Cruciferae are very resistant to ionizing radiation. The inhibition of barley growth induced by X-irradiation was reduced by pre-irradiation treatments with seedling extracts of Brassica napus, B. chinensis or B. juncea. The extracts of seedling of B. B. napus, B. chinensis, B. juncea, B. juncea var. crispifolia, B. oleracea, Raphanus sativus and the extracts of the infloreseences and leaves of Rorippa montana had the similar effect on wheat. The results showed that the radiation resistance of these The reactions of rape extract in qualitative analysis were identical to those of sinapine. Pre-irradiation treatments of wheat and barley seeds with the solution of sinapine thiocyanate crystals extracted from rape showed similar radiation protective effect. The results of ESR spectra of sinapine-thymine binary systems showed that sinapine protected thymine