In this paper, we investigate poly-crystal indium tin oxide (ITO) film produced by a multi-step ion beam treatment on polyethylene terephthalate (PET) at room temperature. In the process of ITO film deposition by a sputtering method, we perform an ion beam treatment after some quantity of ITO deposition is complete, and this process is carried out repeatedly until the required film thickness is achieved. X-ray diffraction indicates that the ITO film deposited by our multi-step ion beam treatment has an almost poly-crystal structure with a morsel of amorphous structure in the PET layers. As a supplementary measurement, a contact angle method shows that the poly-crystal structure is due to a surface charge effect. Consequently, the electrical conductivity of the ITO film (resistivity measurement error bar < 0.7%) with the multi-step ion beam treatment is eight times higher than that of single-treated ITO film, due to this poly-crystal structure. Copyright © 2012 John Wiley & Sons, Ltd.