coatings deposited on polyethylene terephthalate (PET) webs by microwave surface-wave assisted plasma enhanced chemical vapor deposition for the purpose of improving their barrier properties. Oxygen (O ) and hexamethyl- disiloxane (HMDSO) were employed as oxidant gas and Si monomer during SiO x deposition, re- spectively. Analysis by Fourier transform infrared spectroscope (FTIR) for chemical structure and observation by atomic force microscopy (AFM) for surface morphology of SiO coatings demon- strated that both chemical compounds and surface feature of coatings have a remarkable influence on the coating barrier properties. It is noted that the processing parameters play a critical role in the barrier properties of coatings. After optimization of the SiO x coatings deposition conditions, i.e. the discharge power of 1500 W, 2:1 of O :HMDSO ratio and working pressure of 20 Pa, a better barrier property was achieved in this work.