The　objective　of　this　study　was　to　investigate　the　inhibitory　effect　of　the　synthetic　nano-hydroxyapatite　(HA)　on　dental　caries.　The　nano-HA　was　synthesized　by　using　the　depositing　reaction　of　Ca　(H2PO　4)2.　The　artificial　dental　caries　was　made　by　using　sour　solution　and　inoculating　Streptococcus　mutans　(S.mutans)　to　the　Sprague-Dawley　(SD)　rat＇s　mouth　respectively.　After　mineralization　of　solution　of　nano-HA　for　10　days,　the　hardness　of　enamel　was　measured.　The　inhibitory　effect　of　the　synthetic　nano-HA　on　dental　caries　was　detected　by　gargling　way　to　rinse　the　rat　tooth　with　the　solution　of　nano-HA　in　the　animal　test.　Transmission　electron　microscopy　(TEM)　revealed　that　the　dried　HA　particles　were　needle-like　with　φ5-20nm×60nm　and　the　sintered　HA　particles　were　spherical　with　less　than　100nm.　The　remineralized　test　indicated　that　the　solution　of　nano-HA　with　different　shapes　enhanced　the　hardness　of　artificial　caries　and　improved　the　remineralization　of　artificial　caries.　The　animal　test　showed　that　the　dried　nano-HA　had　the　inhibitory　effect　on　dental　caries.　The　good　absorptive　effect　of　the　nano-HA　on　both　the　saliva　protein　and　the　glucans　leads　to　the　development　of　interventions　that　could　reduce　or　modify　bacterial　colonization　of　tooth　surfaces.