This article presents a novel and simple method of liquid-phase exfoliation to fabricate graphene films that possess high conductivity and good light transparency. Graphite was exfoliated in water ethanol mixture, with the aid of Nafion, to give highly stable graphene dispersion. Transparent graphene thin films were easily deposited by vacuum filtration from the Nafion-stabilized graphene dispersion. More important, low-temperature air-annealing (at 250 degrees C for 2 h) was employed to treat freshly-prepared graphene films for the first time. It demonstrates that the technique is advantageous and quite efficient for the fabrication of exfoliated graphite films with defect-free structure and high purity, confirmed by TEM, SEM, FTIR, XPS, and Raman spectra. The resulting graphene films possess a sheet resistance lower than 2.86 k Omega sq(-1) and optical transmittance over 84% at a typical wavelength of 550 nm. (C) 2013 Elsevier B.V. All rights reserved.