A series of sulfonated polyimide copolymers containing 1H-1,2,4-triazole groups in the main chains were synthesized as proton-conducting membranes for fuel cell applications. Polycondensation of triazole-containing dianiline, acid-functionalized benzidine, and naphthalenetetracarboxylic dianhydride gave the title polyimide ionomers. The ionomers were high molecular weight (M-w > 100 kDa, M-n > 20 kDa) to give tough and flexible membranes by Solution casting. The ion exchange capacity (IEC) of the membranes ranged from 1.10 to 2.68 mequiv/g as confirmed by H-1 NMR analyses and titration. Comparison with the other polyimide ionomer membranes revealed that introducing triazole groups caused better thermal stability (decomposition temperature of ca. 200 degrees C), comparable hydrolytic and oxidative stability, and better mechanical properties. Although NH groups did not function as ion exchange sites, the triazole-containing membrane,; showed slightly higher proton conductivity. The highest proton conductivity (0.3 S/cm at 88% RH) was obtained for the high IEC (2.68 mequiv/g) ionomer membrane. The ionomer membranes showed low hydrogen and oxygen permeability under dry and wet conditions.