An optical wiring board and a manufacturing method thereof are disclosed. In accordance with an embodiment of the present invention, the method includes providing a flexible optical waveguide layer, selectively forming a reinforcing clad on one surface of the optical waveguide layer and forming a mirror groove on the other surface of the optical waveguide layer in accordance with where the reinforcing clad is formed. Thus, the clad can be formed thick only on the place where the mirror groove is to be formed, and thus a flexible optical wiring board having flexibility can be manufactured even though the optical wiring board is generally made thin.