Spherical apatite particles were prepared by the homogeneous precipitation method in the presence of magnesium ions. The starting solutions were prepared by mixing 0.167 mol.L-1 of Ca(NO3)(2), 0.100 mol.L-1 of (NH4)(2)HPO4, 1.00 mol.L-1 of (NH2)(2)CO, 0.10 mol.L-1 of HNO3, and a small amount of Mg(NO3)(2). The carbonate-containing apatite powders were obtained by heating these solutions at 80 similar to 95 degrees C for 48 similar to 192 h. Although fibrous particles with long-axis lengths of 30 to 60 mu m were obtained from the magnesium-free solution, spherical agglomerates with diameters of similar to 10 mu m, which contained minute plate-like particles, were present in the apatite powders derived from the solutions with 5 mass% of magnesium ions. The ion-exchange test for the harmful ions (Pb2+, Cd2+, and Ni2+) showed that the ion-exchange abilities of the apatite powders containing magnesium ions were much better than the ability of the magnesium-free apatite powder. The ion-exchanged amounts of the apatite powder containing magnesium ions were arranged in the following order: Pb2+ >> Cd2+ > Ni2+.