The purpose of this study was to determine the solubility of magnesium-containing tricalcium phosphate (MgTCP) over a magnesium content range from 0 to 10 mol%, and to compare it with that of zinc-containing tricalcium phosphate (ZnTCP). MgTCP powders with various Mg contents were immersed in 0.08M acetic acid and sodium acetate buffer solution of pH 5.5 at 25±2 °C. Solubility product, Ksp = (Ca2+)3-x(Mg2+)x(PO4 3-)2, was calculated. From the Ksp data, the solubility of MgTCP in the pH range from 5 to 7.5 was inversely calculated. The solubility of MgTCP decreased with increasing Mg content. The negative logarithm of solubility product (Ksp) was regressed as pKsp = 29.041+0.90467C-0.18069C2+0.025962C3-0.00192C4-0.000055199C5 , where C is the Mg content of MgTCP in mol%. In the magnesium content range from 0 to 10 mol%, the solubility of MgTCP is higher than that of ZnTCP containing the same amount of zinc.