Abstract: In preliminary studies,nano-hydroxyapatite powder which has small particle size and uniform distribution had been synthesized by chemical precipitation method with calcium nitrate and ammonium dihydrogen phosphate as raw mate-rials.To understand hydroxyapatite nucleation mechanism in the process of preparation,crystallization kinetics experiment was designed.Hydroxyapatite supersaturated solution was compounded with calcium nitrate,ammonium dihydrogen phosphate,and ammonia.Conductivity changes of prepared hydroxyapatite supersaturated solution were determined in the process of precipitation,which indirectly reflected ion concentration changes of solution.Nucleation-and growth-rate constant of hydroxyapatite crystallization process were obtained by analyzing data.Results indicated:nucleation rate was far more than growth rate.It was burst nucleation in the instant,which could avoid grain growth for the secondary nucleation.