Abstract: Objective To observe the effect of lobaplatin（LBP）on the radiosensitivity of human gastric cancer cell line BGC823 and the expression of apoptosis-associated protein. Methods MTT assay was employed to obtain the 50％ inhibition concentration（IC50）of LBP on BGC823 cells at 24h after treatment. 20％ of the IC50 dose was treated as sensitizing concentration. The clonogenic assay was used to analyze the cell viability of radiation group and LBP （sensitizer concentration）plus radiation group with X-ray of 0，2，4，6 and 8Gy. The cell survival curve plotted by a single-hit multi-target model was used to analyze the sensitization ratio of LBP. Western blotting and flow cytometry were used to detect the expression levels of apoptosis-related protein（Bcl-2，Bax and cleaved caspase-3）, cell cycle and apoptosis in control group，radiation group and LBP+radiation group after 24h treatment，respectively. Results The IC50 of LBP on BGC823 cells was 16.08μg／ml and the sensitizing concentration was 3.20μg／ml. The cell viability got decreased with increasing radiation dose in radiation group and LBP plus radiation group. The cell viabilities of LBP plus radiation group were lower than those of radiation group at the dose of 4，6 and 8Gy, and the sensitization ratio of LBP was 1.13. There were higher percentage in the G2／M phase，apoptosis rate and levels of Bax and cleaved caspase-3，and lower percentage in the S phase and level of Bcl-2 in LBP plus radiation group versus the other two groups （P＜0.05）. Conclusion LBP can enhance the radiosensitivity of BGC823 cells，induce apoptosis and G2／M phase arrest.