A process for producing a polymer optical waveguide including: 1) preparing a rubber mold having a composite layer structure in which a rubber layer which has a concave portion corresponding to an optical waveguide core and contains a rubber mold-forming curable resin is buried in a rubber layer-forming concave portion of a rigid substrate having the rubber layer-forming concave portion; 2) bringing a cladding substrate into close contact with the rubber mold; 3) filling the concave portion of the rubber mold, with which the cladding substrate has been brought into close contact, with a core-forming curable resin; 4) curing the filled core-forming curable resin; 5) removing the rubber mold from the cladding substrate; and 6) forming a cladding layer on the cladding substrate on which the core has been formed.