The purpose of the present preclinical study was to determine whether vitamin K(2) would promote bone healing in a rat femoral osteotomy model with or without glucocorticoid (GC) treatment. Thirty-eight 6 week-old female Sprague-Dawley rats underwent a unilateral osteotomy of the femoral diaphysis followed by intramedullary wire fixation and then were randomized into four groups that received the following treatment schedules: vehicle, vitamin K(2), GC + vehicle, and GC + vitamin K(2). GC (prednisolone, 2.5 mg/kg) was administered subcutaneously twice a week. Vitamin K(2) (menatetrenone, 30 mg/kg) was administered orally five times a week. After 8 weeks of treatment, the wires were removed and a bone histomorphometric analysis was performed on the bone tissue inside the callus. Vitamin K(2) administration to GC-untreated rats decreased the osteoclast surface/bone surface (OcS/BS), osteoblast surface (ObS)/BS, eroded surface (ES)/BS, and bone formation rate (BFR)/BS and increased the lamellar area/bone area. Although GC treatment increased the ES/BS and decreased the ObS/BS, BFR/BS, and lamellar area/bone area, vitamin K(2) administration to GC-treated rats decreased the OcS/BS and prevented an increase in the ES/BS and a decrease in the lamellar area/bone area. These results suggested that vitamin K(2) downregulated bone turnover and stimulated lamellar bone formation in GC-untreated rats and prevented an increase in bone resorption while maintaining bone formation and prevented a decrease in lamellar bone formation in GC-treated rats. Thus, vitamin K(2) appears to be effective for promoting bone healing in a rat femoral osteotomy model with or without GC treatment.