Indium tin oxide (ITO) thin films were deposited on quartz substrates by direct current magnetron sputtering and annealed in N-2 and air. The normal incidence transmittance of the films was measured by a spectrophotometer. The electrical parameters such as carrier concentration, mobility and resistivity were investigated by van der Pauw method. An optical model has been proposed to simulate the optical constants and thicknesses of the films from transmittance data, which combines the Forouhi-Bloomer model and modified Drude model. The relaxation energy in the Drude term is taken as energy-dependent for a better fitting in the visible spectral range. The simulated transmittance is in good agreement with the measured spectrum in the whole measurement wavelength range. The electrical parameters obtained from the optical simulation are well consistent with those measured electrically by van der Pauw method. The experimental results also indicate that the different post-deposition annealing treatments yield the distinct optical and electrical properties of ITO films. C 2007 Elsevier B.V. All rights reserved.