Plasma polymerization of silane compounds has been discussed for deposition of SiOx positron emission tomography (PET) films at room temperature. A mixture of tetramethoxysilane (TMOS) and oxygen containing 60 mol % O-2 is a preferable raw material for SiOx formation by plasma polymerization. The deposited plasma polymers consist mainly of Si-O networks with small amount of Si-OH and Si-C groups. A part of Si-O networks in the plasma polymers is distorted by the Si-OH and Si-C groups. The oxygen permeability coefficient for the plasma polymer itself is 2.1 x 10(-15) (STP) cm(3)/cm/cm(2)/s/cm Hg, which is lower that that for hydrolyzed ethylene-vinylacetate copolymer(Eval) and poly(vinylidene chloride) (Saran). Conclusively, the plasma polymer deposited from the mixture of TMOS and oxygen containing 60 mol % O-2 is a material with good oxygen barrier properties.