The sheet resistance of the ITO films after oxygen and nitrogen plasma treatments was investigated, based on the change in the lattice characteristics such as the grain size and the lattice strain. The plasma treatment yields an increase in the grain size thence the electrical conductivity in addition to better surface morphology. The decrease in lattice strain is attributable to the increase in the grain size. The experimental results imply that the grain boundary scattering limited mobility plays an important role in the conductivity of ITO films.