The present invention relates to a process for producing an optical waveguide, including the steps of applying a cladding layer-forming resin onto a substrate and curing the resin to form a lower cladding layer; laminating a core layer-forming resin film on the lower cladding layer to form a core layer; subjecting the core layer to exposure to light and development to form a core pattern; and applying a cladding layer-forming resin over the core pattern to embed the core pattern therebeneath, and curing the resin to form an upper cladding layer, wherein the step of forming the core layer includes the steps of (1) allowing the core layer-forming resin film to be temporarily attached onto the lower cladding layer using a roll laminator, and (2) thermocompression-bonding the temporarily attached core layer-forming resin film onto the lower cladding layer under a reduced pressure. There is provided the process for producing an optical waveguide having a uniform core with a good productivity.