Polymeric acid-acid blend membranes comprising of sulfonated poly(ether ether ketone) and sulfonated poly(ether sulfone) were studied at varied water contents ranging from lambda=3 to lambda=15 using MD simulations. Based on the obtained simulation results, blend membranes were found to swell against hydration. With increase in hydration, sulfonic acid groups were observed to become increasingly hydrated which led to increased average distance of sulfur-sulfur, and decreased hydronium ion coordination number around the sulfonic acid groups. By analyzing the water coordination number to water molecules, less developed water phase and less phase separated structure were found for the blend membrane compared to that of Nation. Furthermore, using cluster size distribution analysis for water molecules, it has been understood that large spanning water clusters encompassing all molecules were formed at higher hydrations, which resulted in improved water and hydronium ion transport properties. In comparison with Nation, the simulated diffusion coefficients were smaller in blend membrane. (C) 2012 Elsevier B.V. All rights reserved.