Flat-sheet asymmetric polysulfone (PSF)/polyimide (PI) blended membranes were fabricated by a phase-inversion technique. The fabricated membranes were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, and field emission scanning electron microscopy analyses. The kinetics of thermal degradation of the membranes were studied from thermogravimetric data following Friedman's kinetic approach. The thermal degradation process of the membranes followed first-order rate kinetics, and the activation energy of the thermal degradation process increased with increasing PI content of the membrane compositions. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 3755-3763, 2012