This paper examines processes for the preparation and characterisation of new ceramic membrane materials with potential for gas purification, based on nanostructured anodic alumina. The ultimate research goal is to develop a membrane capable of separating hydrogen from hot synthesis gas so a key factor is the ability of the membrane to operate successfully at temperatures in excess of 800°C. Two membrane materials are compared and contrasted: a commercial Whatman product and a membrane prepared in our laboratory. We have demonstrated that the fabrication conditions, most particularly the acid environment used during membrane fabrication, controls and directs the high temperature behaviour of the membranes. Membranes prepared using sulphuric acid electrolytes have been shown to withstand 800°C without distortion and without compromising their nanostructured pore array.