A method for producing a gas barrier film, the method comprising: biaxially stretching a film base material including a polyester resin having a butylene terephthalate unit as a main constituent unit, wherein in said polyester resin 60% by mass or more of a repeating unit formed by bonding a dicarboxylic acid component and a glycol component is composed of the butylene terephthalate unit; providing an anchor coat layer on the biaxially stretched film base material by coating, wherein the anchor coat layer is further dried; forming at least one metal oxide layer by vacuum film formation on the surface of the anchor coat layer, wherein at least one layer of the metal oxide layer includes at least one of Al and Si; and forming a gas barrier protective layer on top of the metal oxide layer by applying a coating liquid, then heating and drying the coating liquid, wherein the coating liquid contains: a water-soluble polymer; and at least one selected from a group consisting of (a) one or more kinds of metal alkoxide and a hydrolyzate thereof, and (b) tin chloride; wherein the gas barrier film has a tensile elasticity modulus within a range of 2.0 to 4.0 GPa, which is an average value in the MD and TD direction and measured according to the description, and a heat shrinkage rate in the machine direction (MD direction) after heating for 30 minutes at 150°C of less than 3.0%, the heat shrinkage rate being represented by the following formula: Heat shrinkage rate = Length before heating − Length after heating / Length before heating × 100 % wherein the heat shrinkage rate in the MD direction of the gas barrier film is adjusted by controlling the degree of stretching when biaxially stretching the film base material. biaxially stretching a film base material including a polyester resin having a butylene terephthalate unit as a main constituent unit, wherein in said polyester resin 60% by mass or more of a repeating unit formed by bonding a dicarboxylic acid component and a glycol component is composed of the butylene terephthalate unit; providing an anchor coat layer on the biaxially stretched film base material by coating, wherein the anchor coat layer is further dried; forming at least one metal oxide layer by vacuum film formation on the surface of the anchor coat layer, wherein at least one layer of the metal oxide layer includes at least one of Al and Si; and forming a gas barrier protective layer on top of the metal oxide layer by applying a coating liquid, then heating and drying the coating liquid, wherein the coating liquid contains: a water-soluble polymer; and at least one selected from a group consisting of (a) one or more kinds of metal alkoxide and a hydrolyzate thereof, and (b) tin chloride; wherein the gas barrier film has a tensile elasticity modulus within a range of 2.0 to 4.0 GPa, which is an average value in the MD and TD direction and measured according to the description, and a heat shrinkage rate in the machine direction (MD direction) after heating for 30 minutes at 150°C of less than 3.0%, the heat shrinkage rate being represented by the following formula: Heat shrinkage rate = Length before heating − Length after heating / Length before heating × 100 % wherein the heat shrinkage rate in the MD direction of the gas barrier film is adjusted by controlling the degree of stretching when biaxially stretching the film base material.