A novel glassy ionic conductor, lithium niobium oxynitride, was prepared in form of thin films and characterized. Thin‐film deposition was carried out by rf magnetron sputtering of LiNbO3target in nitrogen‐containing atmosphere. These films exhibit ionic conductivity of two orders higher than that of LiNbO3films, the room‐temperature conductivity being about 5×10−7S cm−1. Film structure is highly cross linked, leading to activation energy as low as 0.5 eV. Film transmittance is higher than 85% in both the visible and solar ranges, making them also suitable for use in electrochromic devices. ©1996 American Institute of Physics.