A comparative study of calcination and sintering of hydroxyfluorapatite powders Ca-10(PO4)(6)(OH)(x)F2-x substituted at various fluorine ratios has been carried out. Calcination led to the decrease of the specific surface area by particles coalescence. Superficial diffusion and gaseous phase transport appear as the main mechanisms of surface reduction. For densification a minimum was reached for x = 1 which corresponds to the minimum of FAP-HAP mixing enthalpy. Sintering is limited by the diffusion of hydroxide and fluorine ions.