Gibbsite, which is aluminum oxide, was calcined in the temperature range from 200 to 1150°C, and the relation between the calcination temperature and various properties of gibbsite has been examined. It is speculated based on the results of TG-DTA experiment that the structure of gibbsite changed greatly at a calcination temperature of 282.7°C. Specific surface area of gibbsite kept on increasing as the calcination temperature is elevated up to 400°C, where it reached a maximum value. In the range where the calcination temperature is higher than 400°C, specific surface area decreased as the temperature was elevated further. In addition, it became evident from the results of XRD measurement that in the calcination temperature range lower than 200°C, the crystal kept gibbsite structure, but it changed to the structure of aluminum oxide of transition type above 300°C, and that it changed further to the structure of stable aluminum oxide when the calcination temperature was elevated over 1000°C. From these results, it is verified that by making use of the fact that the structure of gibbsite changes greatly in the calcination temperature range from 300 to 400°C, a novel adsorbent having boehmite structure can be produced. [DOI: 10.1380/ejssnt.2006.267]