Nanosized hydoxyapatite (Ca-10(PO4)(6)(OH)(2) or HA) powders were prepared by a coprecipitation process using calcium nitrate and phosphoric acid as starting materials. The synthesized powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) specific area measurment techniques. Single phase HA, with an average grain size of about 60 nm and a BET surface area of 62 m(2)/g, was obtained. No grain coarsening was observed when the HA powders were heated at 600degreesC for 4 hours. HA ceramics were obtained by sintering the powders at temperatures from 1000degreesC to 1200degreesC. Dense HA ceramics with a theoretical density of 98% and grain size of 6.5 mum were achieved after sintering the HA powders at 1200degreesC for 2 hours. HA phase was observed to decompose into tricalcium phosphate when sintered at 1300degreesC. The microstructure development of the sintered HA ceramics with sintering temperature was also characterized and discussed.