It is well-known that vitamin K has a strong blood coagulation activity by acting a cofactor for gamma-carboxylase which catalizes the conversion of specific glutamic acid residue to gamma-carboxyglutamic acid residue (Gla). Some of the Gla-containing proteins, such as osteocalcin and matrix Gla protein have been found in calcifying tissues. These proteins are considered to play an important role in Ca-deposition. Recent studies have clearly demonstrated the substantial role of vitamin K in bone metabolism that has been developed for clinical use. Furthermore, diverse physiological activities have been found subsequently as follows: regulation of glucose metabolism, anti-arteriosclerosis, and induction of cell differentiation. Here I introduce the mainly physiological activities of vitamin K2, making a comparison with vitamin K1.