Biocompatibility test of nano alumina, has been done by cytotoxicity test method. The crystalline size of nano alumina determined by Rietveld analysis of X ray diffraction studies and Transmission electron microscopy. Cytotoxicity results indicate that cells proliferations has been taken place. So we can conclude that nano alumina is highly biocompatible material. Rietveld analysis of X–ray diffraction and transmission electron microscopy showed that the sample is composed of crystalline and a small fraction of amorphous phases. In view of these, nano alumina may be considered to be future potential for bone substitute material.