Protracted administration of topotecan (TPT), a topoisomerase I inhibitor, exhibited high anticancer efficacy both in animal models and human cancers. This phenomenon is related to the TPT-induced inhibition of angiogenesis in tumor, but the potential mechanism remains largely unknown. In the present study, we reported that TPT (1-10 microM) could inhibit angiogenesis in a dose-dependent manner in Chick embryo chorioallantoic membrane (CAM) assay. TPT showed strong inhibitory activity against proliferation on human EA.hy926 endothelial cells with an IC50 value of 0.13 microM (MTT assay), lower than that of most sensitive cancer cell lines (IC50 range, 0.17 microM to 5.1 microM). TPT could induce EA.hy926 cells undergoing apoptosis, and the percentage of apoptotic cells induced by TPT (0.05 microM-5.0 microM) were 17.9%-52.3%. The similar results were observed with AO/EB staining. Flow cytometry assay also revealed that various concentrations of TPT induced cell cycle disturbance in EA.hy926 cells. Western blotting results showed that TPT caused an obvious increase of p53 expression and a decline of ERK expression in EA.hy926 cells. In addition, the VEGF expression of PC-3 cells is inhibited by TPT in hypoxia. Altogether, inhibiting proliferation of endothelial cells and down-regulating VEGF expression in cancer cells may involve in the antiangiogenesis mechanism of TPT.