Provided is an optical waveguide manufacturing method that makes the thickness of a clad layer in the vicinity of a core portion uniform. A first lamination film is fabricated by forming a clad layer by forming a first curable resin layer for clad formation on a first base film and curing the first curable resin layer, and forming a core portion by forming a second curable resin layer for core formation having a higher refractive index than that of the clad layer after cured on the clad layer and selectively curing the second curable resin layer. A second lamination film is fabricated by forming a clad layer by forming a third curable resin layer for clad formation on a second base film and curing the third curable resin layer. In the optical waveguide manufacturing method, the first lamination film in which the core portion is formed and the second lamination film are bonded together with a fourth curable resin layer for clad formation interposed therebetween, and the curable resin layer interposed between the first lamination film and the second lamination film is cured to form a clad layer.