Provided are a gas barrier resin composition, and a gas barrier composite film excellent in gas barrier properties with respect to oxygen, carbon dioxide gas, water vapor or the like, particularly in gas barrier properties even after hot water treatment. The gas barrier resin composition includes an oxazoline group-containing aqueous polymer (A), an aqueous acrylic resin (B) and/or an aqueous polyester resin (C) each at a specific concentration, wherein the ratio of the mole number of the oxazoline group to the mole number of the carboxyl group [the ratio of the mole number of the oxazoline group (x mmol) to the mole number of the carboxyl group (y mmol), which is indicated as (x/y)×100 (mol %)], is within the specific range. The gas barrier composite film uses this composition.