Objective To evaluate the cytocompatibility of nanophase hydroxyapatite ceramicsinvitro.Methods Hydroxyap- atite(HA) was prepared viawetmethod. The grain size of the hydroxyapatite in the studywas determined by scanning electron mi- croscope and atomic force microscope with image analysis software. Primary osteoblast culture was established from rat calvaria. Cell adherence and proliferation on nanophase hydroxyapatite ceramics and conventional hydroxyapatite ceramics were examined at 1, 3, 5, 7 days. Morphology of the cellswas observed bymicroscope.Results The average grain size of the nanophase and con- ventional HAwas 55 nm and 780 nm, respectively. Throughout 7 days period, osteoblast proliferation on the HA was similar to that on tissue culture borosilicate glass controls, osteoblasts could attach, spread and proliferate on HA. However, compared to conventional ceramics, osteoblast proliferation on nanophase HAwas significantly better after1,3,5 and 7 days.Conclusion Cy- tocompatibility of nanophase HAwas significantly better than conventional ceramics.