Hydrated yttrium oxide and titanium oxide thin films were prepared by reactive sputtering in H 2 O atmosphere at substrate temperatures from %30 to +130°C. The electrical conductivities of the yttrium oxide films increased with decreasing substrate temperature. The increase in electrical conductivity corresponds well to the increase in IR absorption intensity due to OH bonds, and it is considered that proton conduction is dominant in the yttrium oxide films. In contrast, the conductivity of the titanium oxide films increased with increasing substrate temperature, suggesting that electron conduction is dominant in the films.