A gas barrier substrate includes a compound gradient layer. The compound gradient layer includes an inorganic material and a resin material. A content of the inorganic material in the resin material varies in a thickness direction. The gas barrier substrate also includes a gas barrier layer. The gas barrier layer is made of an inorganic material and is bonded to the compound gradient layer. The compound gradient layer has a high content of inorganic material in an area near a bonding surface between the compound gradient layer and the gas barrier layer. The compound gradient layer may be bonded to a resin layer and may have a low content of inorganic material in an area near a surface bonded to the resin layer.