The stability of a gamma-alumina phase incorporated into an a-alumina membrane structure has been studied with regard to the evolution of surface area, pore volume and mechanical integrity, under high temperature conditions. The influence of alkaline dopants on the process of membrane degradation has been studied, as well as the addition of La as a possible stability enhancer. It has been found that the presence of alkaline compounds accelerates the loss of surface area, and the increase in the mean pore radius. It also gives rise to mechanical instability and the formation of cracks, resulting in a sustained increase of the permeation flow across the membrane for a given pressure drop. Doping with lanthanum was not effective in slowing the decrease of surface area; however, it had a positive effect in delaying the phase transformation (gamma to alpha-alumina) that accounts for most of the crack formation observed.