A mold for the formation of an over cladding layer in an optical waveguide is integrally produced from a light-transmissive resin and a light-transmissive support plate by molding using a mold member identical in shape with the over cladding layer. In the production of the mold, a hollow resulting from the removal of the mold member serves as a cavity for the formation of the over cladding layer. For the formation of the over cladding layer, the cavity of the mold 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 in a pattern on a surface of an under cladding layer are immersed in the photosensitive resin.