Nano-crystalline Mg-containing hydroxyapatite (Mg.HAp) were prepared by a wet chemical method, for which selective adsorption of proteins was examined, taking bovine serum albumin (BSA) and a pathogenic protein beta(2)-microglobulin (beta(2)-MG) as the model proteins. Increase in the Mg content led to smaller crystallites and larger specific surface area (SA) of Mg.HAps as well as zeta potential, while the amount both of BSA and beta(2)-MG adsorption on Mg.HAp particles. It is thus concluded that the adsorption of BSA and beta(2)-MG on Mg.HAp was associated with surface charges.