The　oxygen　transmission　rate　(OTR)　of　SiOx　coated　polyethylene　terephthalate　(PET)　and　biaxially　oriented　polypropylene　(BOPP)　affected　by　fine　defects　is　discussed　in　this　paper.　With　an　ultrasonic　AFM　(UAFM),　which　is　an　advantageous　to　distinguishing　tiny　defects　on/in　the　deposited　films,　it　is　found　that　the　OTR　of　the　coated　films　is　relevant　to　the　morphology　scanned　by　UAFM.　Herein　SiOx　layers　with　a　thickness　in　the　order　of　nano-scale　were　fabricated　in　13.56　MHz-radio　frequency　(RF)　-plasma-enhanced　chemical　vapor　deposition　(PECVD).　The　monomer　for　the　coating　fabrication　is　hexamethyldisiloxane　(HMDSO).　Fourier　transform　inferred　(FTIR)　spectra　of　the　deposited　coating　with　a　strong　peak　at　1062　cm＇,　corresponding　to　Si-O-Si　stretching　vibration,　confirm　the　formation　of　SiOx　coatings　through　PECVD.　The　higher　OTR　value　of　SiOx　coated　PET　is　consistence　with　defects　on　film　surface　and　in　the　subsurface　of　coatings　through　UAFM.　It　obtains　that　the　OTR　value　of　the　defect　free　SiOx　coated　film　was　reduced　by　ca.　89%　compared　with　the　defect　existence　SiOx　coated　PET.