Indium Tin Oxide (ITO) films on polyethylene terephthalate (PET) sandwiching TiO2 buffer layers with different sputtering time have been prepared by rf-magnetron sputtering. Scanning Electron Microscope images of the TiO2 buffer layers showed the non-continuous growth in a typical sputtered film growing process. (400) oriented diffraction peaks appeared in all the ITO/TiO2/PET films. The electrical properties were measured by four point probe method and van der Pauw method. The variations of the resistivity and hall mobility on the sputtering time of TiO2 layer were studied. Furthermore, an exponential decay correlation of resistivity and the grain size was fitted. But the linear relationship between the ITO grain size and the mobility indicated by the grain boundary scattering theory didn’t appear here. The reason is believed to neglect the influence of the local variations of the lattice spacing and some other important scattering mechanisms such as lattice, ionized impurity, neutral impurity scattering, etc.