In this study, electrospinning of sulfonated poly(ether ether ketone) (SPEEK) at different degrees of sulfonation (DS) was investigated. The polymer solution concentration of 22 wt% was obtained to collect smooth fiber in nano-scale range of 112 to 131 nm at various conditions. SEM observations of SPEEK nanofibers showed the decrease of diameter with increasing DS from 74% to 81%, mainly due to the increase of electrical conductivity of polymer solution at higher DS. The increase of collecting speed from 20 to 305 m/min decreased the diameter of nanofibers slightly and improved their alignment. The presence of SO3H groups in collected nanofibers was demonstrated with FT-IR analysis. WAXD patterns of SPEEK nanofibers indicated featureless amorphous peak with no crystalline regions that was broaden at higher DS and aligned nanofibers. The electrochemical impedance spectroscopy of SPEEK nanofibers showed the through-plane proton conductivity of fully hydrated nano-fibrous membranes measured at room temperature were improved with DS. The proton conductivity of randomly oriented and aligned nanofibers were measured from 0.0098 to 0.0722 S/cm and from 0.0592 to 0.0907 S/cm, respectively. Aligned nanofibers exhibited more proton conductivity than randomly collected nanofibers. (C) 2016 Society of Plastics Engineers