A successful ablation of Indium Tin Oxide (ITO) coated on PET substrate without damage the substrate is presented in this paper. ITO is a thin film coated on glass and plastic plates as used in flat panel displays (FPD). The conventional machining method is practiced by a wet chemical etching process. This process includes photoresist coating, exposure, development, wet etching, and stripping. Since the ITO coated on PET have the advantages of low cost, less weight, and ductility over than conventional ITO coated on glass. It takes more attentions on this material combination. However, direct-write laser to pattern ITO films on glass has been reported. The ablation of ITO coated on PET is unexplored so far. The experiment of this study uses the KrF ((lambda) equals 248 nm) excimer laser to selectively ablate ITO patterns coated on PET, it generates successful results. Since the excimer laser with short wavelength, high energy density, and short pulse period. It suddenly evaporates the material and minimizes the heat effect on the substrate. The micromachined profile of ITO patterns coated on PET is measured by an atomic force microscopy. The minimum line width can be down to 10 micrometers and avoid any damage to the substrate.