Aim To investigate the effects of sirolimus on proliferation and differentiation of rat smooth muscle progenitor cells(SPC). Methods Total mononuclear cells(MNC) were isolated from marrow of rats by Ficoll density gradient centrifugation method,and then plated on fibronectin-coated culture dishes. Fresh isolated MNC were treated with sirolimus(0.01～100 μg/L) or vehicle control for 12 days.SPC were characterized as adherent cells positive for α-SMA by indirect immunofluorescent staining.After 8 days cultured,attached cells were treated with sirolimus(to make a series of final concentrations: 0.1～200 μg/L) or vehicle control for 24 h.The proliferation and migration of SPC were assayed with MTT and modified Boyden chamber assay respectively.SPC adhesion assay was performed by replating those on fibronectin-coated dishes and counting the adherent cells. Results Sirolimus potently inhibited SPC outgrowth.The number of SPC at 12th day was dramatically decreased by sirolimus.At a concentration as low as 0.1 μg/L,sirolimus significantly reduced(70.9±4.5)% of SPC compared with control(p<0.01).In addition,sirolimus also inhibited SPC proliferative,migratory and adhesive capacity in a concentration-dependent manner. Conclusion Sirolimus could inhibit the proliferation and differentiation of rat smooth muscle progenitor cells.