This manuscript reports, for the first time, a new synthesis route to prepare thermally rearranged microporous polybenzimidazole (TR-PBI) membranes, exhibiting exceptionally highly permeable characteristics to small gas molecules as well as excellent molecular sieving properties. Generally, common PBIs have very rigid, well-packed structures due to their strong intermolecular interactions, resulting in very low gas permeation properties which prevent PBIs from applying in gas separation. Here, we demonstrate new synthesis route to obtain highly permeable TR-PBI membranes having microporous characters (i.e., high fractional free volume), prepared by the alkaline hydrolysis of polypyrrolone followed by simple thermal treatment. (C) 2010 Elsevier B.V. All rights reserved.