The　hydroxyapatite　(HA)　particle　with　different　morphologies　were　prepared　by　adding　a　certain　additive　into　Ca(H2PO4)2　·　H2O　and　controlling　the　bathing　and　sintering　temperature,　and　the　pure　needle-like　HA　sol　were　obtained　when　the　bathing　temperature　was　70C.　The　experimental　results　show　that　the　degree　of　crystallization　of　HA　increase　and　the　particles　tend　to　accumulate　with　increasing　of　the　drying　and　sintering　temperatures.　The　particles　of　HA　were　spheroid,　which　diameters　were　of　less　than　100nm　when　they　were　sintered　at　the　temperature　of　700　°C.　The　effect　of　nano-hydroxyapatite　on　remineralization　of　early　enamel　caries　were　studied　too.　The　hardness　of　dismineralized　enamel　was　increased　when　dismineralized　enamel　was　remineralized　by　nano-hydroxyapatite.　The　SEM　analysis　shows　that　the　interspace　of　enamel　surface　were　decreased　and　the　many　mineral　salts　were　sedimentated,　which　indicated　that　the　nano-hydroxyapatie　could　promote　remineralization　for　the　dismineralized　enamel.　©　2005　Trans　Tech　Publications,　Switzerland.