To investigate the radio-sensitizing effect of artemisinin on U251 glioma cells in vitro, MTT assay, hoechst fluorescent staining, MDC staining, Western blot assay and cloning survival assay were used. The results show that artemisinin can inhibit the proliferation of U251 cells confirmed by MTT assay. The combined treatment with artemisinin and X-rays can significantly increase the apoptosis level in U251 cells studied by hoechst fluorescent staining and induce autophagy confirmed by MDC staining and Western blot assay. Cells previously treated with au-tophagy inhibitors 3-MA, artemisinin and X-rays can decrease number of colonies as compared with combination therapy group (artemisinin + IR). The results suggest that artemisinin can increase the radiation sensitivity of glioma U251 cells by inducing apoptosis. Autophagy can also be induced by treatment with artemisinin and X-rays, and it may play a protective role in the regulation of radio-sensitization of U251 cells.Cited