The mechanism of proton transport of a polymer electrolyte membrane (PEM) with nanomatrix channel was investigated with respect to the activation energy of proton conductivity. The PEM with nanomatrix channel was prepared by graft-copolymerization of styrene onto deproteinized natural rubber (DPNR) followed by sulfonation with chlorosulfonic acid. The resulting sulfonated graft-copolymer (SDPNR-graft-PS) was characterized by FT-IR spectroscopy, solid-state C-13 CP/MAS NMR spectroscopy, elemental analysis, transmission electron microscopy (TEM) and impedance analysis. The PEM was found to form completely continuous nanomatrix channel consisting of natural rubber particle of about 1 mu m in average diameter as a dispersoid and sulfonated polystyrene of about 60 nm in thickness as a matrix. The value of the activation energy of proton conductivity estimated from the slope of Arrhenius plot was 12 kJ/mol for SDPNR-graft-PS, suggesting that the proton transport occurred in a manner of Grotthuss mechanism. (C) 2014 Published by Elsevier B.V.