Abstract: Mice Hepatoma 22 (H₂₂ ) and Lewis Lung Carcinoma (LLC) were used for demonstrating the radiosensitizing effect of shikonin in this study. It was found that for Hss and LLC, the tumor inhibiting rate of shikonin plus radiation group was higher than that by eithor single shikonin or single radiation (P<0.05). And, the tumor growth delay and survival time of tumor-bearing mice of shikonin plus rediation group were also longer than by single shikonia or single radiation (P<0.05). As with LLC, the large necosis was observed in tumor tissue of shikonin ply s radiation group under optical microscope. In addition, ultrastructure observation showed that were some acrophages among tumor cells in shikonin group or shixonin plus radiation group, especially in the latter. The above findings suggest that shikonin has radiosensitizing effect for HZZ and LLC, Beside this, radiation along with shikonin may enhance the capability of macrophages to kill directly tumor cells in LLC, and lengthen the survival time of both Hzz-and LLC-bearjng mice, which may promote indirectly the effect of radiotherapy.