In order to develope hydroxyapatite ceramics which has mechanical strength as bio-implant materials and get the basic data for the study and application of biocompatibility, hydroxyapatite was synthesized at Ca/P=1.67~1.75, pH 7~11 by precipitation method. Using prepared powders, the sintered body, fluorine substituted body and the porous body was formed and their properties were investigated. The sample obtained in condition of Ca/P=1.67, pH 7 and sintering at 1,15$0^{circ}C$ was decomposed to $eta$-tricalcium phosphate, and co-existed with hydroxyapatite. Hydroxyapatite synthesized at pH 11 was not easily decomposed to $eta$-tricalcium phosphate at sintering process. The substitution of a small amount of fluorine for hydroxyapatite prevented hydroxyapatite from being decompsed to $eta$-tricalcium phosphate. Hydroxyapatite ceramics which substited of 10% fluorine was prepared at 1,15$0^{circ}C$, and the valueof bending strength for this body were found to be 112MPa.