Abstract: A support sheet for photographic printing paper having an undercoat layer on which a photographic emulsion layer is to be formed, and which is free from foaming, contamination by foreign substances, and putrefaction and does not effect the photographic emulsion, by the steps of coating front and back surfaces of a substrate sheet with polyolefin resins; surface-activating the front coating layer; and extrusion coating the activated surface of the front coating layer with a coating liquid comprising gelatin, through a slit-shaped orifice, to form the undercoat layer.