The present invention relates to an optical waveguide chip, etc., having a structure for effectively avoiding or suppressing peeling of an optical waveguide layer in a process of cutting a wafer. The optical waveguide chip comprises a substrate having a main surface, and an optical waveguide layer formed on the main surface of the substrate. The optical waveguide layer comprises a cladding portion and a core portion that is disposed inside the cladding portion and that has a higher refractive index than the cladding portion, and at least one of side surfaces of the optical waveguide layer is positioned at a predetermined distance toward a center of the main surface from an edge of the main surface. This arrangement includes an arrangement having a thin film portion at a peripheral region that includes the edge of the main surface. In the case that the optical waveguide layer has the thin film portion at its periphery, the optical waveguide layer has a side surface that coincide with the side surface of the substrate including the edge of the main surface and a side surface that is separated by a predetermined distance from edge of the main surface. By this arrangement, when cutting a wafer into chip units, even if chipping occurs at an edge of the main surface of the substrate to be cut, peeling of the optical waveguide layer, formed on the substrate, is suppressed effectively.