Aqueous solutions of calcium nitrate stabilized with EDTA, ammonium dihydrogen orthophosphate and iron (III) nitrate were mixed before they were subject to ultrasonic spraying and to subsequent pyrolysis in an electric furnace, and particles of 0.45μm in average diameter consisting of hydroxyapatite and hematite were obtained. Surface morphology and microstructure of the particles were examined. A nucleus (hematite)-shell (hydroxyapatite) type structure was observed for larger particles (>0.8μm in diameter) though the particles of medium size apparently had a uniform microstructure. Such structural difference due to the particle size was explained in terms of decomposition of the Ca-EDTA chelating bond at lowest temperatures and temperature distribution in the sprayed mists.