There is provided an optical waveguide including: a waveguide core through which light propagates; a cavity that is present inside the waveguide core so as to be open at least one end in the thickness direction of the waveguide core; a layer-form first cladding having a lower refractive index than the waveguide core, and sealing at least one of the at least one opening of the cavity to thereby close the opening of the cavity; and a second cladding having a lower refractive index than the waveguide core, and surrounding the waveguide core. There is also provided a method of manufacturing the optical waveguide.