In this paper, the effects of H2O2, a typical reactive oxygen species (ROS), on cell proliferation or death were examined using the human cervical carcinoma cell line HeLa and its MDR1-overexpressing subline, Hvr100-6, which was established by stepwise exposure to vinblastine. It was confirmed that the growth of HeLa cells was enhanced by H2O2 at relatively low concentrations in a concentration-dependent manner, and the growth enhancement was suppressed by antioxidants. Doxorubicin and daunorubicin also enhanced the growth of HeLa cells at concentrations lower than IC50 values, and the antioxidants suppressed this effect, being consistent with the fact that both anticancer drugs generate ROS. The growth enhancement by H2O2 or doxorubicin and daunorubicin was not observed in Hvr100-6 cells. In addition, it was suggested that antioxidants had no effect on MDR1 mRNA expression in HeLa and Hvr100-6 cells, and thereby hardly reverse multidrug resistance in tumor cells.