Organicinorganic hybrid gas barrier layers using 3-glycidoxypropyl silsesquioxane with random structures on plastic film were prepared by cross-linking reaction between glycidoxy functional group of 3-glycidoxypropyl silsesquioxane and amino functional group of p-xylylenediamine (PXDA). The effects of PXDA content on the gas barrier property of the membranes were investigated. Oxygen permeability coefficient and water vapor transmission rate of the hybrid layer were the same order of poly(vinylidene chloride). Pencil hardness (750 g load) of the hybrid layers on the polyethylene terephthalate (PET) substrate were HB. The pencil hardness of the PET was B. Thus, the pencil hardness of the hybrid layers was slightly higher than that of PET. These characteristics were attributed to the sufficient dispersion of inorganic segments (siloxane network, SiOSi) and organic segments in the hybrid.