Novel electrospun nanofiber poly(aryl sulfone ether benzimidazole) (SO2-OPBI) membrane is synthesized for enhanced the proton conductivity and chemical stability. Incorporation of the flexible aryl sulfone- and ether-linkages in the polymer backbone are improved the physico-chemical properties of membranes. We prepared different types of membranes, namely dense SO2-OPBI membrane, nanofiber SO2-OPBI and m-PBI membrane and evaluated their physico-chemical properties for suitability application of high temperature PEM fuel cells. Interestingly, the nanofiber membranes possessed a greatly increased proton conductivity (0.0667 S cm(-1) at 160 degrees C and acid doped level of 338%), which is comparable to that of the dense membrane (0.033 S cm(-1) at 160 degrees C and 221% acid doping). The nanofiber and dense membrane shows good oxidative stability under Fenton reagent.