Abstract: Objective To study the effects of breast cancer associated fibroblasts(CAFs)on breast cancer sells in vitro. Methods The CAFs and non-cancer associated fibrolasts(NAFs) were isolated from primary breast tumors and their paired normal breast tissue.The CAFs and NAFs were cultured in 1640 medium without the supplement of serum，and the supernatant were collected.Breast cancer cell lines，MCF-7 and MDA -MB-468 were cultured in the collected supernatant.After 48h of culture，the cells were collected and calculated.Then the cell cycles were tested and the breast cancer stem cell markers CD44 and CD24 were tested by Flow Cytometry. Results We successfully isolated and cultured the NAFs and CAFs.The CAFs increased the expression of α-smooth muscle actin(α-SMA),a defining characteristic of myofibroblasts.The proportion of α-SMA positive cells in NAFs and CAFs were（6.00±0.57）%, （53.33±2.33）%(P<0.001),respectively.The CAFs and NAFs had no effects on breast cancer proliferation in vitro.After 48h of culture，the proportion of G2/M phase of MCF-7 were（5.32±0.02 ）%,（5.63±0.03）%,（6.03±0.03）%(P>0.05)for the control group,NAFs group and CAFs group respectively.Both of the NAFs and CAFs increased the proportion of CD44+CD24-cells in MCF-7 and MDA -MB-468.The proportions of CD44+CD24-cells in MCF-7 were 0.41 and 2.51 folds(P<0.05) higher in the NAFs group and CAFs group respectively than those in the control group.And there were 0.35 and 3.76 folds(P<0.05) higher in the MDA-MB-468 respectively. Conclusion The CAFs induces α-SMA expression，and has no effects on breast cancer proliferation in vitro，although significantly increases the rates of cancer stem cells.The CAFs might play an important role in the progresses of cancer recurrence and metastasis.