Pt, and Pt oxide thin films were prepared by reactive sputtering of Pt in Ar and O-2 gas mixtures, and the influence of O-2 flow ratio On their formation process was studied. O-2 gettering by Pt atoms was confirmed from plasma emission spectra and pressure change in a sputtering chamber before and, after striking the discharge. At O-2 flow ratios below 20%, almost all of the introduced O-2 molecules were gettered and Pt films were deposited. At O-2 flow ratios above 20%, the number of supplied O-2 molecules overcame the gettering effect and the O-2 partial pressure began to increase, and Pt oxide films were deposited. The deposition rate of Pt oxide films decreased at O-2 flow ratios above 30%, because the target surface state changed from a metallic target mode to an oxide target mode.