Calcium phosphate nanoparticles were prepared by hydrothermal treatment of several types of calcium salt and phosphate aqueous solution. Crystalline phase and particle morphology of as-prepared particles were influenced by types of starting solution. Homogeneous hydroxy Apataite (HAp) nanoparticles were obtained by a hydrothermal treatment of CaCl₂-Na₂HPO₄- NaOH aqueous solution. X-ray fluoreseence analysis showed the Ca/P ratio of HAp nanoparticles was 1.67. The use of alternative combination of calcium salts and phosphate led to the formation of HAp with calcium phosphate, dibasic, anhydrous (DCPA) or calcium phosphate, dibasic, 2-hydrate (DCPD). The pH of starting solution influenced the ones unit of crystalline phase in the nanoparticles. The aspect ratio of HAp particles decreased with increasing concentration of starting solution.