Hydrogen-radical durability of TiO2 thin films has been investigated under conditions for preparing Si thin film solar cells by catalytic chemical vapor deposition method. It is found that the composition and the optical transmittance of TiO2 films are almost the same before and after hydrogen-radical exposures with a filament temperature at approximately 1700 degreesC and a H-2 pressure of approximately 133 Pa. The durability of TiO2 film has also been observed even under the condition with higher hydrogen-radical density under a filament temperature at approximately 1900 degreesC, in which SnO2 and ZnO are easily deoxidized. The application of TiO2 film as a protecting material of transparent conducting oxide film for Si thin film solar cells are discussed by the hydrogen-radical durability and fundamental properties of TiO2 thin film. (C) 2003 Elsevier Science B.V. All rights reserved.