Abstract: Objective: In order to gain basic experimental data for clinical targeted therapy of breast can -cer, we studied the inhibi ting effect of rosigl i tazone (the peroxisome prol i ferator-activated receptor γ activator) combined with 5-aza-2'-deoxycytidine (a demethylating agent inhibitor) on the MCF- 7 cell line in vitro.Methods: Fully-developed MCF- 7 cells were inoculated in 24-well tissue culture plates at 2.0 × 10 6 /L. MTT assay was used to observe the inhibiting effect of rosiglitazone and5-aza-2’-deoxycytidine on the growth of MCF- 7 cells. Changes in morphology were observed using inverted microscopy. We used flow cytometry (FCM) to ex -amine the apoptosis rate and percentage of cells in each stage of the cell cycle. Results: MTT assay results showed that the growth of MCF- 7 cells treated with rosiglitazone or 5-aza-2’-deoxycytidine or a combination of the two agents were effectively inhibited compared with the control group (P<0.05). The inhibitory rate was increased as time went by. At 72h after treatment, the apoptosis rates of cells in early cell cycle in the rosigli -tazone group, the 5-aza-2'-deoxycytidine group, the combination group and the control group were 36.9% , 22.7%,35.5% and 24.1%, respectively. The apoptosis rates of cells in late cell cycle in the four groups were 16%,43.7%,37.7% and 40.2%, respectively. The percentages of cells in G0 and G 1 phases combined in the rosiglitazone group, the 5-aza-2'-deoxycytidine group, the combination group and the control group were 81.3% ,67.3% ,74.5% and 6% , respectively. The percentages of cells in S phase in the above four groups were 2.5%,17.1%,0% and 38.5%, respectively. The percentages of cells in G2 phase were 16.3%,15.6%, 25.5% and 55.4% , respectively. Compared with cells in the control group, cells in G0 and G 1 phase were blocked by rosiglitazone,5-aza-2'-deoxycytidine or the combination of the two agents ( P<0.05). Combination of the two agents did not enhance the cell cycle blocking effect or the apoptosis rate ( P<0.05). Conclusion: Rosiglitazone and5-aza-2'-deoxycytidine can effectively inhibit the growth of human breast cancer cell line MCF-7. Rosiglitazone has a cell cycle blocking effect and 5-aza-2’-deoxycytidine interferes with cell cycle, possibly through induction of cell maturation and differentiation.