The effects of menaquinone-4 (MK-4; vitamin K₂) supplemented egg shell calcium ( Cal K ₂) on bone components in the femoral-diaphyseal (cortical bone) and -metaphyseal (trabecular bone) tissues of rats was investigated. Cal K ₂ contained calcium carbonate (Ca 100 mg/g) and MK-4 (593 μ g/g). Rats were orally administered a solution of Cal K ₂ (10, 25, or 50 mg/ml/100 g body weight) or placebo (without MK-4, 50 mg/ml/100 g body weight) once daily for 7 days. The serum r -carboxylated osteocalcin concentration, which is produced in osteoblastic cells, was significantly increased after the administration of Cal K ₂ (50 mg/100 g body weight) as compared with that in the control group or placebo-control group without MK-4. Calcium content and alkaline phosphatase activity in the femoral-diaphyseal tissues were significantly increased after Cal K ₂ (25 or 50 mg/100 g) as compared with that in the placebo-control group. Femoral-metaphyseal calcium content was significantly increased after the administration of Cal K ₂ (25 or 50 mg/100 g) as compared with that in the control group. DNA content in the femoral-diaphyseal and -metaphyseal tissues was significantly increased after the administration of Cal K ₂ (50 mg/100 g) as compared with that in the control or placebo-controlled group. This study demonstrates that the oral administration of Cal K ₂ containing MK-4 has anabolic effects on bone components in rats. Supplemental Cal K ₂ may have a role in the prevention of bone loss with aging.