Abstract: AIM To isolate and identify smooth muscle progenitor cells ( SPCs) from rat bone marrow and observe specific expression profile of the smooth muscle progenitor cells during proliferation and differentiation in vitro. Methods MNCs were isolated by ficoll density gradient centrifugation from rat marrow and cultured in conditioned nutrient chemical, identification was performed by immunofluorescent staining (α-SMA,CD14).And smooth muscle cells specific markers (α-SMA) were determined with Western blotting and Real-time PCR at different time. Results During culturing, cells adhered and became spindle shaped with outgrowth at 4 d and 7 d ,and presented typical "peak" "valley" at 14 d (3 generation). Both α-SMA and CD14 were positive after 4 d. Expression for α-SMA was not found at 1 d with Western blotting,but it gradually enhanced at 4 d and reached to the top from 10d to 14 d ,and still remained high-level at 21 d .The results with Real-time PCR indicated that the expression of α-SMA mRNA within non-induced cells was not found ,but after being induced it gradually enhanced at 4 d and got to peak at 14 d, and still remained high-level at 21 d , low-expression at 1 d was significantly different from the other ones (P<0.01). Conclusion SPCs could be isolated and cultured from rat marrow monocytes, and proliferated, differentiated into smooth muscle -like cells.