AIM: To investigate multi-potential of rat bo ne marrow mesenchymal stem cells (rBMMSC) and mutation inclination, the rBMMSC w ere long passaged in vitro. METHODS: Cellular cycles of diff erent passages were assayed by FA CSan flow cytometry and karyotypes of passage 6, passage 25 and passage 45 were compared by G-binding analysis. RESULTS: The early passages and long-term passages all showed st rong proliferation; passage 6, passage 25 and passage 45 all showed normal karyo type. CONCLUSION: Long-term culture and passage of rBMMSC still remain s strong proliferation. With this capability, the mutation inclination is not enhanced.