A method of manufacturing an optical waveguide includes forming a core layer on a first clad layer, forming a second clad layer on the core layer, forming a first groove including at least one inclined surface in the second clad layer and the core layer to be in substantially parallel to and near one end of the second clad layer and one end of the core layer, the at least one inclined surface of the first groove having such an angle that the core layer is exposed when viewed above the second clad layer, forming a second groove including at least one inclined surface in the second clad layer on a inner side of the first groove, forming a separation groove in the clad layers and the core layer in a direction intersecting the first groove, and forming a plurality of cores intersecting the first groove.