The ion-transport properties of the tungsten trioxide (WO3)-, WO3/polyaniline (PAn)-, and WO3/PAn polyvinylsulfate (PVS)-confined electrodes have been studied by means of the in situ Fourier transform infrared (FTIR) spectroscopic method. In highly acidic solution (pH = 0), (WO3)-O-VI, was reduced to (HxWO3)-O-V by the reaction with H3O+ and the generated H2O molecules were incorporated in the film, but in solutions of pH greater-than-or-equal-to 2, the reduction of (WO3)-O-VI, was attained by the reaction with H2O and the concentration of H2O decreased in the film. The charge-compensating reaction for the reduction of WO3/PAn films in solutions of pH greater-than-or-equal-to 2 depended on the electrode potential. In the potential range between + 0.2 and - 0.2 V versus Ag/AgCl, the reduction of the positively charged PAn was achieved by expelling anions without the accompanying injection of cations into WO3. In the potential range between - 0.3 and - 0.8 V, however, WO3 and the charged PAn were simultaneously reduced by protons. PVS remained doped at the WO3/PAn/PVS-confined electrode during potential cycling, and the charge-compensation was accomplished by involving cations.