AIM To gain insight into the biochemical mechanisms of Topotecan induced apoptosis in leukemia cells. METHODS The cytotoxic effect of Topotecan on HL 60 cells was measured by using MTT assay; Topotecan induced apoptosis in HL 60 cells was identified by morphological analysis, DNA agarose gel electropheresis and Annexin V FITC staining; correlation between Topotecan mediated apoptosis and caspase activation was investigated by caspase 8 or caspase 3 inhibitor. RESULTS After incubated with 0 1 ?mol?L -1 TPT for 8,12 and 16 h, survival rate in HL 60 cells significantly reduced to 62%?12%( P