A series of sulfonated polyimide/poly (vinyl alcohol-co-vinyl acetate) (SPI/PVA-co-PVAc) composite membranes was facilely prepared from blending SPI salt with 80% hydrolyzed PVA-co-PVAc in m-cresol followed by casting. A miscible system of the prepared composite membranes was confirmed by scanning electron microscopy (SEM). Properties required for a proton exchange membrane, such as ion exchange capacity, water uptake, dimensional change, hydrolytic stability, proton conductivity, and methanol permeability, were measured and investigated in detail. The bound water distribution of the composite membranes was found to increase with PVA-co-PVAc contents due to the formation of the H-bonding between absorbed water and hydroxy groups of PVA-co-PVAc. In a direct methanol fuel cell (DMFC) test, an increase of PVA-co-PVAc in the composite membranes enhanced the cell performance of blend membranes. The composite membrane yvith 25 phr PVA-co-PVAc loading has shown high power output with 6 M methanol feed at a cell operating temperature of 80 degrees C. (C) 2013 Elsevier B.V. All rights reserved.