The present invention provides a coating agent, wherein an oxygen-barrier property enhancer, which is one or more of glucose, mannose, maltose, trehalose, fructose, raffinose, arabinose, nigerooligosaccharide, lactose, D-glucono-1,5-lactone, arginine hydrochloride, ferrous sulfate, sodium dihydrogen phosphate, mannitol, Palatinit, and vitamin C, is added to acid-treated yeast cell wall fractions consisting of cell residue obtained by removing the internal soluble cell components of enzyme-treated yeast, the residue being treated with an acidic aqueous solution to further remove the solubilized components, and which enables a film being formed by coating with the coating agents for an oxygen permeability test by using the coating agent to attain at 23.degree. C. and relative humidity of 60% an oxygen permeability coefficient of<0.1 cm.sup.3 mm/m.sup.2atm 24 hr.