The　purpose　of　this　study　is　to　examine　the　inhibitory　effects　of　nano-HA　on　the　caries-inducing　properties　of　a　four-organism　bacterial　consortium　in　vitro.　A　series　of　in　vitro　anticarious　experiments　have　been　carried　out　by　using　a　continuous　culture　system.　Streptococcus　mutans,　Streptococcus　sanguis,　Actinomyces　viscosus,　Lactobacillus　rhamnosus　have　been　chosen　as　the　experimental　bacteria.　After　48　hours,　the　dental　plaque　surface　structure　is　observed　with　the　scan　electron　microscope　and　the　bacterial　colonization　was　evaluated　on　dental　plaque.　The　results　show　that　Spherical　nano-HA　and　mixed　nano-HA　are　proved　to　be　effective　in　anticarious　experiments,　and　especially　spherical　nano-HA　is　more　striking.　It　is　able　to　damage　the　formation　of　biofilms　(dental　plaque),　postpone　or　end　the　process　of　acid　generation　of　bacteria　metabolism.　After　7　days,　the　demineralization　of　the　enamel　has　been　detected　by　using　TEM.　The　spherical　nano-HA　might　have　a　remineralization　to　early　caries　to　prevent　and　decrease　caries.