The mechanism and kinetics of hydroxyapatite (HAP) precipitation from aqueous solution at the conditions of pH 10-11 and at calcium ion concentrations of more than 0.5mol/l were investigated. The results show that the reaction undergoes the following process: transferring from octacalcium phosphate (OCP) to amorphous calcium phosphate (ACP) rapidly, and then from ACP to calcium-deficient hydroxyapatite (DAP) and HAP. DAP was the non-stoichiometric material that ACP converts to HAP. Reaction temperature greatly affects the reaction rate of the conversion from ACP to HAP. It takes about 24h to form pure-phase HAP at 25 o C while it takes only 5min at 60 o C. The temperature also has a great deal of influence on the particle size and morphology of precipitated hydroxyapatite. The reaction of transformation from ACP to DAP was second order and the activation energy was 95kJ/mol (22.7kCal/mol) and therefore it was inferred that the conversion reaction was a surface control process.