The moisture effect on conductivity of graphene oxide (GO) films was studied. GO films of 200-500 nm thickness become conductive (Omega ranges from 10(6) to 10(2) S/cm) upon the moisture increase from 30% to 100%. Waters diffusion changes the films morphology. The UV reduction of GO reduces the film sensitivity toward moisture until the complete disappearance. Proton character conductivity is concluded for GO, the isotopic effect for the conductivity being sigma(H)/sigma(D) = 1.4 +/- 0.1. The GO film conductivity increases in polar solvents vapors (alcohols, acetone, pyridine, etc.), however, nonpolar (toluene and hexane) and chlorine containing (CCl4, CHCl3) solvents vapors do not affect the conductivity. (C) 2013 Elsevier B.V. All rights reserved.