A series of experimental methods including MTT test, alkaline phosphatase (ALP) activity measurement, oil red 0 stain and measurement and mineralized function were employed to assess the effects of Y(3+) on the proliferation, differentiation, adipogenic transdifferentiation and mineralization function of primary mouse osteoblasts (OBs) in vitro. The results indicated that Y(3+) (1x10(-9), 1x10(-8), 1x10(-7), 1x10(-6), 1x10(-5), and 1x10(-4) mol/L) promoted the proliferation of OBs on day 1, 2 and 3. Y(3+) had no effect on the differentiation of OBs at concentrations of 1x10(-9) and 1x10(-8) mol/L, promoted the differentiation of OBs at concentration of 1x10(-7) mol/L, but turned to inhibit the differentiation of OBs at other tested concentrations on day 1. On day 2, Y(3+) inhibited the differentiation of OBs at all tested concentrations. On day 3, Y(3+) promoted the differentiation of OBs at lower concentrations of 1x10(-9) and 1x10(-8) mol/L, but turned to inhibit the differentiation of OBs at other concentrations. Y(3+) promoted the adipocytic transdifferentiation of OBs at most tested concentrations on day 9 and 12. On day 15, Y(3+) promoted the adipocytic transdifferentiation of OBs at lower concentrations of 1x10(-9) and 1x10(-8) mol/L, turned to inhibit at other tested concentrations. Y(3+) inhibited the formation of mineralized matrix nodules of OBs at concentrations of 1x10(-9), 1x10(-8) and 1x10(-6) mol/L, but turned to promote the formation of mineralized matrix nodules of OBs at other tested concentrations. These findings suggested that the effects of Y(3+) on the proliferation, differentiation, adipocytic transdifferentiation and mineralization function of primary OBs depended on the concentration and culture time, moreover, concentration and culture time were pivotal factors for switching the biological effects of Y(3+) from toxicity to activity, from damage to protection, or from down-regulation to up-regulation.