Polymer-inorganic nanocomposite membranes present an interesting approach to improve the separation properties of polymer membranes because they possess properties of both organic and inorganic membranes such as good permeability, selectivity, mechanical strength, and thermal and chemical stability. The preparations and structures of polymer-inorganic nanocomposite membranes, their applicability to gas separation and separation mechanism are reviewed. (c) 2007 Elsevier B.V. All rights reserved.