A novel sulfonated diamine bearing aromatic sulfophenyl pendant groups, named as, 2,2'-bis(4-sulfophenyl)-4,4'-oxydianiline (SPhODA) was synthesized. Sulfonated (co)polyimides (SPIs) with flexible ether linkage in the main chain and sulfopheryl groups in the side chain were synthesized from SPhODA, 1,4,5,8-naphthalene tetracarboxylic dianhydride and nonsulfonated diamines. The SPI membranes showed good solubility in common aprotic solvents and high desulfonation temperature of 320 degrees C. The SPIs with ion exchange capacities of 1.57-2.50 meq g(-1) displayed reasonably high proton conductivities of 0.09-0.21 Scm(-1) at 60 degrees C in water and 0.02-0.05 Scm(-1) at 70% relative humidity. They also displayed high mechanical properties, but their water stability was not enough high at high temperatures. They showed high potential for DMFC application at low and/or mediate temperatures. (c) 2009 Elsevier B.V. All rights reserved.