There is a closely relationship between vitamin K and osteoporosis. As a cofactor for carboxylase activity, vitamin K can facilitate the conversion of glutamyl to gamma-carboxyglutamyl residues and influence the synthesis and excretion of gamma-carboxylation of osteocalcin to increase the formation of bone. Vitamin K can also effectively inhibit the absorption of bone mass. Besides, there are increasing evidences that vitamin K can effect the synthesis and excretion of nephrocalcin and interlukin-1,6 that can regulate calcium balance and bone metabolism. Meanwhile, there is a consistent line of evidence in human epidemiologic and intervention studies that clearly demonstrate that vitamin K can not only increase bone mineral density in osteoporotic people, but also reduce fracture rates to improve bony health. However more researches are required before vitamin K is widely applied in prevention and treatment of osteoporosis. The American Medical Association recently has increased the dietary reference intakes of vitamin K to 90 mg/d for females and 120 mg/d for males.