Parameters and/or processes responsible for the stability of catalyst supports and ceramic membranes are discussed. Two major parameters/processes were identified which are responsible for the stability of sol-gel defined nanostructured oxides at elevated temperatures. They are metastable-to-stable phase transformation and structure and packing of primary particles within the aggregate. Based on these observations, strategies to develop thermostable nanostructured oxides for high-temperature membrane and catalyst applications are discussed by taking titania and titania-alumina nanocomposites as examples.