We have developed an X-ray magnification radiographic system incorporating a microfocus X-ray tube and an imaging plate in order to analyze the trabecular structure and mineral content of rat bone. Femoral bones of control, ovariectomy, and leuprorelin acetate depot rat groups were extracted and tested after the animals were sacrificed. Eleven water-equivalent phantoms, which contained hydroxyapatite at a density of 0 to 400 mg/cm3, were set around each femur and radiographed at the same time. The mean read-out signal intensity of the region of interest in the femur was converted to bone mineral density expressed in hydroxyapatite density through the use of a calibration curve relating the signal intensity to the hydroxyapatite density of the phantoms. The bone mineral density of the ovariectomy group was significantly lower than that of the control group, and no differences were found between the control and the leuprorelin acetate depot group. The present system is thought to be useful for quantitative evaluation of the mineral density of the rat femur.