Thin films of molybdenum-doped indium oxide (IMO) were prepared by a 3-source, cylindrical radio-frequency magnetron sputtering at room temperature. The films were post-annealed and were characterized by their structural (X-ray diffraction) and optical (UV-VIS-NIR spectrophotometer) properties. The films were studied as a function of oxygen volume percentage (O2 vol.%) ranging from 3.5 to 17.5. The structural studies revealed that the as-deposited amorphous films become crystalline on annealing. In most cases, the (222) reflection emerged as high intensive peak. The poor visible transmittance of the films as-deposited without oxygen was increased from ∼12% to over 80% on introducing oxygen (3.5 O2 vol.%). For the films annealed in open air, the average visible transmittance in the wavelength ranging 400-800 nm was varied between 77 and 84%. The films annealed at high temperatures (N300 °C) decreased the transmittance to as low as b1%. The optical band gap of the as-deposited films increased from the range 3.83-3.90 to 3.85-3.98 eV on annealing at different conditions.