An optical waveguide device includes a plurality of optical waveguides extending adjacent each other in a sheet-like form. Each of the waveguides includes core portion, an inner cladding layer formed on a periphery of the core portion, and an outer cladding layer formed on a periphery of the inner cladding layer. The inner cladding layer is devoid of light scatterers, whereas the outer cladding layer has light scatterers disposed therein. As light travels within the core portion, such light is efficiently reflected at the surface of the inner cladding layer. The outer cladding layer having the light scatterers disposed therein functions to inhibit crosstalk between adjacent waveguides.