The present invention provides a bidirectional communication optical waveguide which can adopt a configuration in which light sources having the same wavelengths are used and stray light is not inputted to either a light emitting device or a light receiving device, and the bidirectional communication optical waveguide realizes a bidirectional communication module. The bidirectional communication optical waveguide includes a main waveguide core and a sub-waveguide core. A main inclined plane is provided in a midway of an optical path in the main waveguide core.