Indium molybdenum oxide (IMO) films were made from an oxidized target with In2O3 and MoO3 in a weight proportion of 95:5 by using a high density plasma evaporation (HDPE). Hydrogen was added to the Ar+O-2 gas mixture during the preparation of the IMO films. With hydrogen, the decrease in the resistivity and the broadening of the process window was mainly due to an apparent increase in the mobility The transmittance in the visible spectral range of IMO films deteriorated with the incorporation of hydrogen. Mo+6/Mo+4 species, -OH fragment, metallic Mo and Mo-O oxides in the film were suggested to affect its electrical and optical properties. Applications as transparent and conducting films for opto-electronic and telecommunication devices would be expected in the near future. (C) 2004 Elsevier B.V. All rights reserved.