The maximum substitution of monovalent, divalent, and trivalent metal ions for beta-tricalcium phosphate (beta-TCP) was investigated, and a substitution model of these metal ions for beta-TCP was proposed. Monovalent metal ions (M-I) could replace Ca(4) site and vacancy (V-Ca(4)) in beta-TCP as 2M(I) = Ca2+ + V-Ca(4) and the maximum substitution was about 9.1 mol%. In the case of divalent metal ions (M-II), Ca(4) and Ca(5) sites were replaced by divalent metal ions as M-II = Ca2+, and the maximum substitution was about 13.6 mol%. Trivalent metal ions (M-III) could be substituted for Ca(4) site and vacancy as 3M(III) = 2Ca(2+) + V-Ca(4), and the maximum substitution was about 9.1 mol%.