Abstract: Objective : To compare the anti-cancer activity of pirambicin, adriamycin, and epirubicin, on three breast cancer cell lines, MCF-7, T-47D, and Bcap-37, and to study their time-effect relationship. Methods :ATP based tumor chemosensitivity assay (ATP-TCA) was used to establish the in vitro dose-effect and time-effect curves. The ability of these three drags to induce apoptosis of the three cell lines was detennined by Annexin V apoptosis assay method. Results : The inhibition of the three drugs on the growth of MCF-7, T-47D, and Bcap-37 was dose-dependent. THP exhibited a stronger growth inhibition than adriamycin and epirubicin on three breast cancer cell lines, respectively. 50% inhibiting concentration (IC50) of THP for three cell lines was significantly lower than adriamycin and epirubicin (P<0.01), while the latter two drags showed no statistical difference (P>0.05). The inhibitory effects of three drugs on breast cancer cells were time dependent. THP at low concentration exhibited growth inhibition on breast cancer cells rapidly (12-24h); while retarded effect was observed in adriamycin and epirubicin treated groups with 10-20% higher tumor survival rate than THP group. Increased apoptotic ratio of cancer cells was noted in all drug-treated groups, while THP treated group exhibited higher apoptotic ratio than that of the other two drug-treated groups. Conclusions : THP exhibited excellent activity of both growth inhibition and apoptosis induction on breast cancer cells. It' s recommended for further clinical study in breast cancer treatment.