Abstract: Objective To investigate the effect of trastuzumab, a special blocker of epidermal growth factor receptor-2(HER-2) on proliferation and apoptosis of human umbilical vein endothelial cells (HUVECs) exposed to tumor conditioned medium(TCM). Methods HUVECs were cultured and exposed to TCM, and trastuzumab was used as an intervention. Then their proliferation, apoptosis and cell cycle distribution were measured by MTT and flow cytometery(FCM). Intra-tumor microvessel density (MVD) and HER-2 expression were tested by immunohistochemistry(IHC). Results Following the stimulation of MDA-CM, HUVECs showed higher proliferating and anti-apoptotic ability(P<0.05). Trastuzumab relieved the above roles significantly((P<0.05), while trastuzumab didn't affect HUVEC's growth directly. Among 35 cases of breast invasive ductal carcinoma, 19 cases were HER-2 negative with an area density of MVD (0.72±0.77 and count density(33.83±0.11/mm2), 16 cases were positive with a relative higher value( 0.74±0.11 and 36.42±5.65/mm2 respectively), the discrepancy has no significance. Conclusion Trastuzumab could decrease the proliferating and anti-apoptotic role on endothelium induced by TCM from MDA-MB-231.