Effects of static magnetic fields (SMF) on bone formation of rat femurs, were evaluated using tapered rods made of magnetized and unmagnetized samarium cobalt of the same size. They were implanted transcortically into the middle diaphysis of rat femurs under press-fit loading. The bone mineral density (BMD) and bone calcium content were measured 12 weeks after implantation by dual-energy X-ray absorptiometry and chemical analysis with o-cresolphthalein complexon, respectively. The result revealed that the femurs adjacent to magnetized specimens had significantly higher BMD and calcium content than those adjacent to the unmagnetized specimen (p < 0.01). However, the value of BMD and calcium content of rats with magnetized specimens was similar to that of non-operated rats. No specific change was found in the body weight, serum Ca, activity of alkaline phosphatase, hemogram, and BMD of the tibia and humerus among the magnetized and unmagnetized. These results suggest that the long-term local SMF stimulation on the bone has a local effect to prevent the decrease in BMD caused by surgical invasion or implantation.