A method of fabricating an optical waveguide which comprises forming a core layer (c) on surface of a peelable substrate (a), then forming a clad layer (d) on the surface of the core layer (c) and the surface of the substrate (a), and then peeling the substrate (a) off from the core layer (c) and the clad layer (d) to fabricate an optical waveguide of which the top face (e) or the bottom face of the core layer (c) is not covered by the clad layer (d).