A production method of an optical waveguide for a connector is provided, which reduces an optical coupling loss. Cores are formed in a crossing pattern, a branched pattern or a linear pattern, and then an over-cladding layer formation photosensitive resin layer is formed over the cores. In turn, a heat treatment is performed at a temperature of 70° C. to 130° C. to properly form mixed layers in interfaces between the cores and the photosensitive resin layer. By thus forming the mixed layers, the connector optical waveguide can be produced as having a reduced optical coupling loss.