Objective To investigate the effects of kidney-tonifying Plastrum Testudinis on o steogenesis of cultured rat mesenchymal stem cells(MSCs ).Methods MSCs were isolated from adult rats wi th density gradient separation meth od.Osteogenesis of MSCs in the culture a dded with different concentrations of serum containing Plastrum Testudinis was evalu-ated by detecting bone glaprotein(BGP)level and observing the morphologic al features of MSCs and by alkaline ph os-phatase(ALP)and Von Kossa immunohistochemical m ethods.Results Morphological examination showed t hat the MSCs attachment formed soon after seedin g ,and grew into colonies with the appearance of fibroblastic cells.Seru m containing Plastrum Testudinis promoted the expression of alkaline phosphatase(ALP)in MSCs ,and increased BGP level and the number of calcified deposition in dose -dependant manner,the difference being significant in comparison wi th the control groups(P