The effects of long-term extremely low-frequency magnetic field (ELF-MF) exposure on bone formation and biochemical markers were investigated in ovariectomized rats. Sixty mature female Sprague-Dawley rats were randomly divided into four different groups (n = 15): (i) unexposed control (CTL); (ii) ovariectomized only (OVX); (iii) non-ovariectomized, exposed (SHAM + ELF-MF); and (iv) ovariectomized, exposed (OVX + ELF-MF). The third and fourth groups were exposed to 1.5 mT ELF-MF for 4 h a day for 6 months. Bone mineral density (BMD) was determined using dual energy X-ray absorption (DEXA) measurements. The formation and resorption of bone were evaluated using bone-specific alkaline phosphatase (BAP), osteocalcin, osteoprotogerin, and N-telopeptide. After 6 months of ELF-MF therapy, BMD values were significantly lower in the OVX group and higher in the OVX + ELF-MF and SHAM + ELF-MF groups than they were before therapy (P < 0.001). Although there was no significant difference in BMD values among the groups before therapy, the BMD values increased significantly after 6 months in the OVX + ELF-MF and SHAM + ELF-MF groups and were reduced in the OVX group compared to the CTL group (P < 0.001). The concentrations of BAP, osteocalcin, osteoprotogerin, and N-telopeptide in the three experimental groups also changed in a significant way compared to the CTL group. The results of the present study suggest that osteoporosis can be inhibited by ELF-MF stimulation treatments. It was also concluded that ELF-MF may be useful in the prevention of osteoporosis in ovariectomized rats.