Diffuse reflectance infrared Fourier transform and Raman spectroscopy is applied to investigate the structure of hydrolyzed CaHPO4 . 2H(2)O (DCPD) processed to non-stoichiometric apatite to be used as starting material for preparing sintered calcium phosphate materials. The spectra of hydrolyzed DCPD samples, obtained under differing experimental conditions, are analyzed to check how the sintered phase composition correlates with the structure of the hydrolyzed precursor. It is shown that the addition of extra Ca2+ ions in the alkaline solution during the process of hydrolyzing affects strongly the degree of disorder in the structure of the hydrolyzed materials, thus increasing the relative amount of hydroxyapatite in the final sintered product. The addition of F- ions to the synthesis mixture strengthens slightly the P-O bonds in the precursors and increases the content of hydroxyapatite phase in the sintered material. As a result bi-phase ceramics of highest content of hydroxyapatite can be produced using both fluorine additives and calcium compensators in the synthesis suspension.