Abstract: To observe the effect of the selenium with different concentrations on the morphology, proliferation and viability of mice osteoblast in vitro. The 24 hourold mice osteoblasts, which were obtained from skull with complete enzyme digestion, were cultured in DMEM solution seperatively containing various concentrations of sodium selenite（0.00，0.05，0.1，0.2，0.4，0.6，0.75，1.0 mg/L）. The morphological changes were viewed; The proliferation rate and cell viability were measured by MTT and crystal violet staining, respectively. The results indicated that the proliferative capacity and viability of osteoblasts exposed to Na2SeO3, was increased at the concentration of 0.2 mg/L in 48 h, however they were inhibited over 0.4 mg/L Na2SeO3. Selenium has two-side effects for proliferation and viability of osteoblasts. It is time-dossage dependent.