The purpose of this research was to investigate the effects of petroleum ether extract of Euonymus alatus (EAP) on the proliferation of human tumor cells. EAP inhibited the proliferation of HeLa, Hep G2, KHOS/NP and A431 cells. The cytotoxicity of doxorubicin on human tumor cells and Balb/c 3T3 cells were increased by the combination of EAP. EAP did not affect the proliferation of Balb/c 3T3 cells, mouse spleen cells and human lymphocytes. These results suggest that EAP has the cytotoxicity on human tumor cells without cytotoxicity on Balb/c 3T3 cells, mouse spleen cells and human lymphocytes, and increase the cytotoxicity of doxorubicin.