Abstract： Objective To investigate the effect of endothelial progenitor cell (EPC) on regulating proliferation and apoptosis of bone marrow mesenchymal stem cell (BMSC) in the indirect co-culture system.Methods BMSC and EPC were cultivated and identified in vitro.Using transwell inserts to establish EPC and BMSC indirect co-culture system.Experimental groups were prepared as follows:BMSC/EPC indirect co-culture:BMSC were co-cultured with EPC that were separated in transwell insert.Control:BMSC/BMSC were indirect co-cultured at the same cell counts with the experimental groups.Colony forming unit-fibroblast(CFU-F) assay was studied with three types of EPC/BMSC ratios (1∶1,10∶ 1,100∶1) to assess the capacity and efficiency for cell self-renewal.In addition,flow cytometry technique was used to detect the cell cycle at co-cultured 3 days and the cell apoptosis at co-cultured 3,7,10 d.Results Under indirect co-culture condition,EPC could significantly promote cell cycle progress and enhance capacity of cell self-renewal.Co-cultured EPC resulted in an accumulation of BMSC at S phase [experimental group:(15.72 ±2.93)％,control group:(2.02 ±0.66)％,P ＜0.01].CFU-F assay showed that the self-renewal capacity of EPC:BMSC/10:1 group [(50.98 ± 6.32) ％] and 100 ∶ 1 group [(57.87 ± 14.06) ％] were significantly higher than that in control group [(33.07 ± 9.60) ％ and (30.06 ± 7.20) ％] (P ＜ 0.01).However,EPC had a slight but non-significant down-regulated effect on BMSC apoptosis (P ＞ 0.05).Conclusions Under indirect co-culture condition,EPC could enhance the proliferation of BMSC,but could not regulate cell apoptosis in vitro.