Background: Mesenchymal stem cells (MSCs) are adult, multipotent, stem cells with immunomodulatory properties. One of the mechanisms used by MSCs to perform such action is its ability to increase the number of CD4+CD25+FOXP3+ Tregs invitro . In the present work we tried to investigate the capacity of BM-MSCs to increase the number of Treg cells after co-culturing with PBMNCS from SLE and normal subjects under appropriate culture condition. Methods: MSCs were cultured from 4 bone marrow samples in appropriate culture medium and isolated when they became at least 70-80% pure. PBMNCs were obtained from 14 SLE subjects as well as 7 healthy subjects. Treg markers (CD4+CD25+FOXP3+) were measured by flow-cytometry before and after 7 days of co-culture with MSCs. Results: MSCs were successfully isolated from bone marrow samples, identified by morphology, adherence to plastic flasks and by flow-cytometric characterization of their surface expression of MSCs markers. MSCs were able to increase the percentage of CD4+CD25+FOXP3+ T regs significantly after co-culture with PBMNCs from both SLE patients and normal subjects. Conclusion: This study demonstrated that MSCs may contribute to the generation of an immunosuppressive environment via the induction of Treg cells. This result might have important clinical implications for autoimmune diseases.