A method of manufacturing an optical waveguide is provided in which a mold that prevents fins or burrs from being formed is used for the formation of an over cladding layer in the optical waveguide. The mold for the formation of the over cladding layer is produced from a light-transmissive resin by molding using a mold member including a protruding portion identical in shape with the over cladding layer and a ridge portion provided around the protruding portion. For the formation of the over cladding layer, the cavity is filled with a photosensitive resin for the formation of the over cladding layer, and the photosensitive resin is cured by being exposed to light through the mold while cores formed on a surface of an under cladding layer are immersed in the photosensitive resin and part of the photosensitive resin spilling out of the cavity is collected in the groove.