Hydrothermal corrosion of TiN, TiAlN and CrN PVD films (3 μm thick) deposited on SUS-304 substrate was studied in 100MPa water in 20-950°C temperature range up to 750h. The beginning temperature of their reaction was determined as 200°C for TiN and TiAlN and 500°C for CrN films, which are quite low in comparison with that of air oxidation of those powders. Very thin oxide scales of TinO2n-1 homologous series phases were formed above 300°C. TiO2anatase is observed for TiN and TiAlN films at 400°C. The feature of hydrothermal corrosion of CrN films seems to be CrNxOy phase formation. Distinguishable weight changes were observed at higher temperature than 700°C for TiN, 750°C for TiAlN and 800°C for CrN respectively. Hydrothermal corrosion kinetics was constructed to calculate the activation energy of hydrothermal corrosions. On the base of obtained data, hydrothermal corrosion resistance was as follows: TiN → TiAlN → CrN. Facetted oxide crystals were formed at higher temperature than 500°C for TiN, TiAlN and 850°C for CrN.