Thin films of Ta3N5 and TaON prepared on Ta foils are examined in terms of surface composition and stability in air and in water to evaluate the effectiveness of these materials as visible light-responsive photocatalysts for water oxidation and reduction. The Ta3N5/Ta film is formed by nitridation of Ta2O5 on Ta foil at 1123 K under NH3 flow (greater than or equal to20 mL min(-1)), while the TaON/Ta film is formed from the same precursor but with heating at 1073-1123 K under an NH3 flow of 10 mL min(-1). The surface of the Ta3N5 film is found to contain oxygen species including hydroxyl groups, and TaON exhibits a higher oxygen content than the stoichiometric amount. X-ray photoelectron spectroscopy reveals that the surface of the Ta3N5 thin film becomes partially hydrolyzed in water, while the TaON film surface remains stable with respect to hydrolysis even in water.