Abstract: Objective 　To investigate the cytotoxicity and proapoptotic activity of topotecan ( TPT) on cisplatin - resistant human ovarian cancer cell lines COC1/ DDP and its mocular mechanisms. Methods 　The cytotoxicity of TPT on COC1/ DDP was monitered using MTT assay and sof t agaragar assay. TUNEL and flow cytometry were employed to observe the apoptosis of COC1/ DDP induced by topotecan. Western blot were used to determine the expression of bcl-2, bax and caspase-3, in addition to the activity of caspase-3. Results 　TPT had strong cytotoxicity on COC1/ DDP cell in vit ro, and the cytotoxicity was dose-and time-dependent . TPT treated cells demonst rated apoptosis property while the apoptotic rate was increased from 8. 54 % to 23. 16 %( P < 0. 05) . Although the expression of bcl-2 was not affected, the expression of bax and caspase-3 were upregulated and the caspase-3 activity was promoted in the course of COC1/ DDP apoptosis when t reated with topotecan. Conclusion 　The cytotoxicity and proapoptosis activity of TPT, which is significantly observed in cisplatin-resistant human ovarian cancer, may be related to the increased bax expression and the promoted caspase-3 activity.