Aim To investigate the feasibility of differentiation of bone marrow mesenchymal stem cell(BMSC) into smooth muscle cell(SMC) in vitro under platelet-derived growth factor-BB(50 μg/L) and high concentrations of fetal bovine serum(FBS)(20%),and the positive effect of myocardin on BMSC differentiating into SMC.Methods Mouse BMSCs were isolated and purifed from bone marrow,then 50 μg/L PDGF-BB and FBS(20%)were added to the BMSCs.And the cells were cultuted for 4 and 8 days respectively.Immunohistochemistry assay and image analysis were used to value the exptession extent of α-smooth muscle actin(α-SMA),smooth muscle myosin heavy chain(SM-MHC)and myocardin.Results Intensities of the three protein immunostaining significantly increased after 4 and 8 days.And Test of One-way ANOVA showed that there was statistically significance in different times(P<0.05).Conclusions BMSC could be induced to differetiate into smooth muscle-like(SM-like) cells through adding PDGF-BB(50 μg/L) and FBS(20%) with BMSC in vitro.Myocardin may play an important role in this process.