Abstract: Objective: To study the effect of docetaxel (DOC) combined with 4-AP on human breast can -cer MCF-7 cells and to explore whether 4-AP could strengthen the effect of docetaxel.Methods:MTT assays were performed to investigate the effect of docetaxel, 4-AP and the combination of them on the proliferation of MCF-7 cells. Flow cytometry was employed to detect cell cycles and cell apoptosis after the cells were stained by PI alone or by Annexin-V and PI. Results: Docetaxel could significantly inhibit the proliferation of MCF-7 cells in a dose- and time- dependent manner. 4-AP could inhibit the proliferation of MCF- 7 cells and the inhibitory rates were 11.9%±1.7%,42.1%±3.2%, and44.2%±1.6% at24h, 48h and 72h after adding4-AP. Moreover4-AP (5mmol/L) could strengthen the effect of docetaxel. 4-AP (25μ mol /L) could increase the effect of Docetaxel. Docetaxel at5 μ mol /L could signi ficantly increase the percentage of cel ls at G2/ M (53.58% ± 1.44% vs.8.83%±0.44%,P<0.01) and decrease the percentage of cells at G0/G1 (11.48%±0.14% vs.63.89%±0.98% ,P<0.01), indicating that docetaxel blocked MCF- 7 cells at G 2/M phase. 4-AP at 5mmol/L could in-crease the percentage of MCF-7 cells at G0/G1 and decrease the percentage of cells at G2/M ( 0.42%±0.17% vs. 8.83%±0.44%,P<0.05). Docetaxel could significantly increase late apoptosis and death of MCF- 7 cells af-ter treatment over 24h (from6.97%±0.75% to20.77%±0.75%,P<0.05). Docetaxel combined with 4-AP could increase early apoptosis rate from 4.60%±0.91% to12.20%±0.82% (P<0.05) and could increase late apopto -sis rate and death rate from 4.60%±0.91% to12.20%±0.82% (P<0.05). Conclusion:Both docetaxel and 4-AP can inhibit the proliferation of MCF- 7 cells. Docetaxel can increase the percentage of cells at G 2/M phase and 4-AP can increase the percentage of cells at G 0/G1 phase.4-AP could strengthen the inhibitory effect of docetaxel on the proliferation of MCF- 7 cells through inducing cell apoptosis.