Matrix gla protein (MGP) is a protein found in numerous body tissues that requires vitamin K for its optimum function. It is present in bone (together with the related vitamin K-dependent protein osteocalcin), as well as in heart, kidney and lung. In bone, its production is increased by vitamin D.

MGP and osteocalcin are both calcium-binding proteins that may participate in the organisation of bone tissue. Both have glutamate residues that are post-translationally carboxylated by the enzyme gamma-glutamyl carboxylase in a reaction that requires Vitamin K hydroquinone. This process also occurs with a number of proteins involved in coagulation: prothrombin, factor VII, factor IX and factor X, protein C, protein S and protein Z.