Zwitterion-coated graphene oxide (ZC-GO) containing ammonium and sulfonic acid groups was synthesized, and various amounts were incorporated into polybenzimidazole (PBI). The effect of the ZC-GO content on the properties of PBI/ZC-GO composite membranes for direct methanol fuel cell (DMFC) applications was investigated. The structure of ZC-GO was confirmed using Fourier transform infrared spectroscopy, and the purity and structure of FBI were investigated using proton nuclear magnetic resonance spectroscopy. With increasing ZC-GO content, the proton conductivity, methanol permeability, water uptake, and swelling ratio of the composites increased, whereas the thermal stability decreased. Notably, the composite membrane containing 25 wt% ZC-GO exhibited a high proton conductivity (4.12 x 10(-2) S cm(-1) at 90 degrees C and RH 100%) and low methanol permeability (1.38 x 10(-7) cm(2) s(-1) at 25 degrees C), which is much lower than that of Nafion 117 under the same conditions. The excellent properties of the composite membranes can be attributed to the homogeneous dispersion of ZC-GO and the formation of proton transport channels in the membranes. This investigation demonstrates the potential of PBI/ZC-GO composite membranes for DMFC applications. (C) 2015 Elsevier B.V. All reserved.