Pt-graphene (Pt-G) is prepared by in-situ reduction of Pt precursor on graphene oxide surface using a microwave method. Various Nation/xPt-G/ySiO(2) composite membranes where x is 0.5 wt%, 1.5 wt% and 3.0 wt% and y is 0.0 wt%, 1.5 wt% and 3.0 wt%, respectively are fabricated of which water uptake and proton conductivity show similar trend: that is, those are increased with both Pt-G and SiO2 contents. The cell performance is significantly affected by relative amount of Pt-G and SiO2 in composite membrane. Below 1.5 wt% in Pt-G content, the cell performance is increased with SiO2 due to the excellent retention ability of SiO2 for water produced from Pt site on graphene. Beyond 1.5 wt% in Pt-G content, however, the cell performance is rather decreased compared to that of 1.5 wt% Pt-G. It is ascribed to the blocking effect for proton conduction due to too much inorganic tiller and possible loss of electrons through Pt network. The effect of SiO2 on cell performance seems to be different depending on Pt-G and relative humidity (RH). Open circuit voltage (OCV) is significantly affected by SiO2 content and increased with SiO2 content. (C) 2014 Elsevier B.V. All rights reserved.