The invention provides a method for manufacturing an optical waveguide device, with which the thickness of an optical substrate can be controlled with high precision. The surface of a substrate is masked by applying a resist to all regions of the substrate except where stopper portions are to be formed (i.e. to the left and right in width direction of the substrate). Then, the stopper portions are formed on the surface of the substrate by sputtering/vapor deposition of Cr, and then the resist is removed. Using a UV curing resin, an Mg-doped LiNbO₃ optical substrate is laminated between the pair of stopper portions to the left and right of the surface of the substrate. After laminating the optical substrate, which is made of a non-linear optical material, the optical substrate is abraded.