To provide a water-based coating composition that has a high concentration, a low viscosity and high storage stability as well as excellent gas barrier properties.

The objective water-based gas-barrier coating composition comprises (A) 100 pts.wt. of a copolymer composition mainly containing (meth) acrylic alkyl ester and (B) 40-200 pts.wt. of polyvinyl alcohol with a saponification degree of ≥93 mol.%. In another embodiment, the water-based gas-barrier coating composition includes 5-20 pts.wt. of boric acid per 100 pts.wt. of the polyvinyl alcohol resin on the solid basis. This invention further relates to methods of producing the coating compositions.