It is not possible to press the molding die (34) onto the under-cladding layer (32) by the application of a high pressure because the quartz-made molding die (34) has a weak mechanical strength. This makes it easier to create a clearance (42) between the molding die (34) and the under-cladding layer (32). A method for manufacturing an optical waveguide which comprise the steps of: filling an ultraviolet curable liquid-state resin (17) to form an over-cladding layer (14) in a concave portion (16) of a die (15), wherein the thickness of the over-cladding layer is thicker than a designed layer; bringing an under-cladding layer (12) and a core (13) into close contact with the ultraviolet curable liquid-state resin (17) filled in the concave portion (16) of the die (15); and irradiating ultraviolet rays (24) from a substrate (11) side after bringing the under-cladding layer (12) into close contact with the die (15) by the application of a pressure (23) onto the substrate (11) and the die (15) to cure the ultraviolet curable liquid-state resin (17) and then removing the die (15).