In this paper, the sulfonated poly(phthalazinone ether ketone) (SPPEK) nanofibers with low sulfonation degree are fabricated by electrospinning for the first time. The optimized concentration of SPPEK for electrospinning is 0.16 g ml(-1) and the suitable solvent is the mixture of DMAc and NMP. The resulting SPPEK nanofibers show smooth surfaces and uniform diameters of about 50 nm. Proton conductivities of the SPPEK mat and membrane are tested and compared. The result indicates that the proton conductivity of the SPPEK mat is almost five times as high as that of the SPPEK membrane because of the formation of long-range proton pathways on the surfaces of SPPEK nanofibers. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4581-4586, 2013