Objective: To evaluate the antitumor effect of PDOX on breast cancer MCF-7 cells, and to assess the cytotoxicity of PDOX on normal human hepatic cell line LO2 and mice renal tubal epithelium cell line NRK52E. Methods: Breast cancer MCF-7 cells were treated with different concentration of DOX or PDOX for indicated time, the half maximal inhibitory concentration (IC 50) of DOX and PDOX were calculated for comparison; normal hepatic cell line LO2 and mice renal tubal epithelium cell line NRK-52E were treated with the identical concentration gradient of DOX or PDOX, and the cytotoxic effect of DOX or PDOX on LO2 cells and NRK52E cells were compared; cell cycle distribution of MCF-7 cells was analysed by flow cytometry after being treated with identical concentration of DOX and PDOX; MCF-7 cells were treated with the identical concentration of DOX and PDOX, then the post-treatment morphology was determined by TdT-mediated dUTP nick end labeling (TUNEL), apoptotic cell Hoechst stain. Results: At 48 h, the IC50 of DOX and PDOX for MCF-7 cells were 0.94, 3.91 μM respectively; At 72 h, the IC50 of DOX and PDOX for MCF-7 cells were 0.63, 1.62 μM respectively. In vitro studies showed that PDOX had reduced cytotoxicity on LO2 cells and NRK52E cells compared with DOX; PDOX mainly arrested cell cycle of MCF-7 cells at G1/S phase. After PDOX and DOX treatment, MCF-7 cells revealed typical morphological characteristics and DNA fragmentation. After being treated with 1.96, 3.91 μM DOX or 1.96, 3.91 μM PDOX for 48 h, the apoptotic rates were 46.1%, 61.1%, 41.3% and 48.1%, respectively. Conclusion: In vitro, PDOX had lesser anti-tumor effect on MCF-7 cells than equivalent DOX. Compared with DOX, PDOX had reduced cytotoxicity on LO2 cells and NRK-52E cells.