To obtain a gas barrier coating agent which can satisfy such various requirements, for example, sufficient oxygen barrier property and sufficient adhesiveness to various substrate plastic films, as having not been achieved by conventional polyvinyl alcohol resin-inorganic compound composite coating agents.

This coating agent is characterized by mixing an inorganic laminar compound with a resin prepared by grafting a monomer having a reactive double bond and carboxyl group on a polyvinyl alcohol-based resin. A coated product is obtained by coating a substrate with the coating agent.