Three types of calcium phosphate ceramics, i.e. tricalcium. phosphate, biphasic calcium phosphate and near stoichiometric hydroxyapatite, were prepared by sintering at 1200degreesC for 2 h in air with moisture protection. Their dissolution processes were investigated by taking micro structural observations after immersion in distilled water for 3 or 7 days. It was found that the surface dissolution of the ceramics was initiated at grain boundaries and generated many separated grains. In case of the materials with high porosity, the residual pores on the surface appeared to be a primary defect site where the dissolution starts although the soluble compound was existed on the matrix.