As an antireflection coating material a Ta2O5film is deposited onto the surface of Au for Au‐CdS solar cells by vacuum evaporation in the presence of O2at a total gas pressure of about 10−4–10−5Torr. The reflectance is measured in the spectral region from 330–600 nm. It is found that the optimum thickness of Ta2O5film for 200 A˚ of Au thickness is 1220 A˚, in which case the minimum reflectance is approximately zero at 480 nm. On both sides of the minimum value the reflectance rises steeply. For a fixed thickness of Ta2O5the position of wavelength at minimum reflectance has a slight tendancy to move to a longer wavelength with increasing thickness of Au film.