Objective To observe the effects of low dose irradiation (LDR) on proliferation,adipogenesis and osteogenic potential of human umbilical cord mesenchymal stem cells (hucMSCs).Methods hucMSCs were isolated from Wharton's jelly tissue of human umbilical cord by modified tissuepiece inoculation,and flow cytometry was used to detect the expression of specific marker in the hucMSCs.The hucMSCs were randomly divided into two groups:irradiation group undergoing irradiation with the doses 50,100,or 200 mGy respectively,and control group without irradiation.MTT method was applied to evaluate the proliferation of the hucMSCs at different time points with various doses irradiation.The third passage hucMSCs were randomly divided into two groups:irradiation group undergoing low dose irradiation of 200 mGy,and control group without irradiation,and then underwent induction by adipocytic and oesteocytic differentiation induction fluids respectively so as to differentiate into adipocytes and osteoblasts.Oil red O staining was used to detect the activity of alkaline phophatase (ALP),and RT-PCR was used to detect the mRNA expression of core binding factor alpha 1 in human osteoblast.Results After 9-12days,fibroblasts began to swim out of the tissue piece with a confluence rate of 80% 2 weeks later.Within 7 days the absorption values of the hucMSCs undergoing different irradiation doses 2,3,4,5,and 6 days later were all significantly higher than those of the control group(F = 159.17,448.81,265.15,183.93,and 181.83 ,all P <0.01),with the proliferation rates of the 100 mGy subgroup being the highest.After being induced liquid,vacuoles were observed in the irradiated group 2 days later.21 days later,the adipogenic rates of irradiated group was significantly higher than that of the control group (t = 28.25,P <0.01).The ALP activity increased in the irradiated group compared with control group (t=16.87,P <0.01) .The expression level of Cbf-α1 mRNA was up-regulated obviously (t = 14.16,P＜0.01).Conclusions LDR promotes the proliferation of hucMSCs,and accelerates the hucMSCs' differentiation into adipocytes and osteoblasts.