To investigate the radiation effect on Notch pathway in osteoblast and osteoblast differentiation, the expression of Notch1 and Runx2 were analyzed. Osteoblast differentiated from Bone marrow stromal cells (BMSCs) was analyzed by real-time PCR and western blot after 2 Gy or 4 Gy 137Cs γ-irradiation. Notch1 mRNA (p<0.05) and protein expression level were up-regulated after 4 Gy irradiation. 2 Gy and 4Gy irradiation increased Runx2 mRNA (p<0.05) and protein expression level. ALP mRNA (p<0.01) and protein expression level were repressed by 2 Gy and 4 Gy irradiation. These results indicated that up-regulated Notch1 could inhibit osteoblast differentiation after irradiation of 4 Gy. Further more, up-regulated Runx2 expression did not repressed Notch signaling after irradiation of 4 Gy.Cited