In this paper we reported that nano-scale SiOx layers deposited on polyethylene terephthalate (PET) foils by microwave surface-wave plasma-enhanced chemical vapor deposition for purpose of improvement of their barrier properties. Oxygen (O2) and hexamethyldisiloxane (HMDSO) were employed as oxide gas and precursor, respectively, in this work for SiOx deposition. Analysis by fourier transform infrared spectroscope (FTIR) for chemical structure and atomic force microscopy (AFM) for morphology of SiOx layers demonstrated that both chemical compounds and surface feature of coatings have a remarkable effect on the coating barrier properties. A permeation parameter of oxygen transmission rate (OTR) of 1.35 cc/m2.day.atm for SiOx coated 12.5 um PET foils, i.e. decreasing ca. 100 times compared to control sample (130 cc/m2.day.atm) was achieved. The dependency of process parameters, such as the ratio gas mixture, input power, working pressure, and coating thickness on oxygen permeation through PET foil were explored in the whole process.