In this study, ITO films were deposited by an oxygen ion beam assisted evaporation technique on glass and polycarbonate substrates at room temperature and the effects of oxygen radical on the properties of ITO thin films were investigated. To generate oxygen radicals, in addition to one oxygen ion gun irradiating oxygen ions to the substrate during the ITO deposition, a separate oxygen ion gun was used without applying any Voltage to acceleration grid and extraction grid while varying rf power to the ion gun. The increase of rf power to the gun increased the number of oxygen radicals. The increase of oxygen radicals to the oxygen ion beam assisted evaporation of ITO increased the optical transmittance of the ITO deposited on both glass and polycarbonate substrates. The conductivity of the deposited ITO also increased with the increase of oxygen radicals, however, too many oxygen radicals decreased the conductivity of the ITO. Hall measurement showed that the change of the carrier concentration in the film was responsible for the change of the resistivity. The increase of optical transmittance and the change of electrical conductivity with the increase of oxygen radicals were related to the oxygen incorporation to the deposited ITO thin film. ITO deposited on the polycarbonate substrate showed a little lower optical transmittance and conductivity possibly due to the higher surface roughness of the substrate. We were able to obtain room temperature ITO thin him on glass with 5.5 x 10(-4) Omega cm and above 85% transmittance (at 550 nm) and that on polycarbonate with 6.0 x 10(-4) Omega cm and approximately 85% transmittance (at 550 nm).