The invention provides a method for producing a polymer optical waveguide equipped with a plurality of alignment marks (AM), which comprises bringing a film substrate into contact with a mold having concave portions corresponding to convex portions for the optical waveguide and convex portions for a plurality of AMs, introducing a curable resin from an end of the mold into concave portions, curing the resin, peeling the mold, and forming a cladding layer on a core/AM-forming surface, or bringing a film substrate into contact with the mold having concave portions corresponding to convex portions for the optical waveguide and notches, introducing the curable resin from an end of the mold into the concave portion, curing the resin, applying a material for AM to the film substrate through the notches and, thereafter, forming the cladding layer on the core/AM-forming surface.