The relationship between the uses of antiepileptic drugs (AEDs) and the risk of fractures have been reported. While, there is only limited data concerning the effects of the newer AEDs on bone metabolism. In this study, we investigated the effects of gabapentin, a newer antiepileptic drug on bone metabolism. Male SD rats were administrated with gabapentin (30, 150 mg/kg) orally every morning for 12 weeks. Bone histomorphometry was analyzed using a semiautomatic image analyzing system, and bone strength was evaluated using a three-point bending method. Bone mineral density was measured using quantitative computed tomography, and serum biochemical markers (osteocalcin, tartrate-resistant acid phosphatase-5b) were examined. Administrated of gabapentin significantly decreased bone volume and increased trabecular separation, as shown by bone histomorphometric analysis. Moreover, the bone formation parameters, osteoid volume and mineralizing surface, were decreased after gabapentin treatment, whereas the bone resorption parameters, osteoclast surface and number, were increased. These results suggested that gabapentin may act on bone metabolism through the suppression of bone formation and enhancement of bone resorption.