A series of carbonated hydroxyapatites containing sodium ions with variable amounts of carbonate were precipitated. Chemical analyses, infrared absorption spectrometry, X-ray diffraction patterns and thermogravimetry with gas chromatography analyses were performed. The results show two decomposition temperature intervals. These intervals correspond to dehydration and decarbonation processes. The latter phenomenon takes place in two steps. The first one corresponds to CO32- B type and the second one to CO32- B and A type decomposition processes.