A gas barrier sheet improved in a gas barrier property and a manufacturing method thereof are provided. A gas barrier sheet includes at least a base material and a gas barrier film provided on the base material which allows a ferromagnetic element to be present at the boundary of the gas barrier film on the side at which the gas barrier film 3 faces the base material. The ferromagnetic element is preferably present in a scattered form, an island form or a thin film form at a boundary.