Abstract: The graphene oxide (GO) was synthesized by the modified Hummers' method, then GO and Ca(NO₃)₂ and (NH₄)₂HPO₄ were prepared to synthesize the GO/nano hydroxyapatite (nHAP) composites powder by simultaneous titration method. The morphology, phases, chemical groups and element valence of the GO/nHAP composites powder were investigated by TEM, XRD, FTIR and XPS, and the biological performance of GO/nHAP composite powder was examined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. The results show that the nHAP in the GO/nHAP composites appears drusy acicular crystal structure and disperses evenly. The size of drusy acicular crystals is about 50-100 nm, and the size of graphene oxide sheets is 1 000-4 000 nm. nHAP nucleates in situ on the surface of the GO and grows along the (112) plane preferentially, and the two phases are bound to each other by chemical bonds. The GO/nHAP composites powder exhibit no cytotoxicity.