In order to elucidate the action of La3+ on bone metabolism, effects of La3+ on the osteogenic and adipogenic differentiation of primary mouse bone marrow stromal cells (BMSCs) were studied by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) test, alkaline phosphatase (ALP) activity measurement, mineralized function, oil red O stain and measurement. The results showed that La3+ promoted the proliferation of BMSCs except at 1x10(-10) and 1x10(-6) mol/L. The effect of La3+ on the osteogenic differentiation depended on concentrations at the 7th day, but the osteogenic differentiation was inhibited at any concentration at the 14th day. La3+ promoted the formation of mineralized matrix nodules except at 1x10(-8) and 1x10(-5) mol/L. La3+ inhibited adipogenic differentiation except at 1x10(-10) and 1x10(-7) mol/L at the 10th day, and inhibited adipogenic differentiation except at 1x10(-9) mol/L at the 16th day. These findings suggested that La3+ might have protective effect on bone at appropriate dose and time. This would be valuable for better understanding the mechanism of the effect of La3+ on bone metabolism.