A series of proton conducting, thin-film solid electrolytes, based on poly(vinyl alcohol), trifluoromethane sulfonic. acid and water (PVA-CF3SO3H-H2O) were prepared by the casting technique. The polymer electrolytes were transparent with a slightly brownish coloration. Maximum conductivity is obtained for samples containing about 40 wt.% of PVA, 36 wt.% of CF3SO3H and 24 wt.% of water, and reaches a level of ca. 10(-2) S/cm at room temperature. The temperature dependence of the conductivity indicates the Arrhenius-type behaviour of the system for all compositions of the PVA-CF3SO3H-H2O electrolytes, with activation energy of 30 kJ/mol (0.31 eV).