Transformations in In-MoO 3 nanosystems have been studied by optical spectroscopy, micros copy, and gravimetry in relation to the thickness of the In and MoO 3 layers and heat treatment temperature and time. We have measured the contact potential difference across the In and MoO 3 films and the photo voltage in the In-MoO 3 system and constructed the energy band diagram of the In-MoO 3 system. A model has been proposed for the thermal transformation of the MoO 3 films in In-MoO 3 bilayers, which involves a redistribution of equilibrium charge carriers at the contact, the formation of a [(V a ) ++ e] center during the preparation of the MoO 3 film, transformation of the center into a [e(V a ) ++ e] center during the fabrication of the In-MoO 3 bilayer, and thermal ionization of the [e(V a ) ++ e] center.