Unsupported alumina membranes were prepared by sol-gel technique using aluminum isoproxide. The influence of the hydrolysis conditions, the type and concentration of peptizant acid on the boehmite sols has been studied. The suitable hydrolysis temperature for the aluminum isoproxide was above 50 degrees C. Crack-free unsupported alumina membranes were obtained by rapid gelation processing of sols. The boehmite gel membrane and gamma-Al2O3 membrane formed exhibited (020) and (440) preferred orientation.