Abstract: An optical waveguide device and a method of making the same that render excellent transmission loss characteristics and allow a large degree of freedom in circuit design are provided. The method has the steps of forming a fluorine-added silica glass first cladding layer on a substrate, forming a silica glass protective layer on the first cladding layer, annealing, forming a groove that penetrates through the protective layer and reaches the first cladding layer, forming a silica glass core in the groove, and forming a fluorine-added silica glass second cladding layer on the protective layer and the core. The device has a substrate, a first cladding layer formed on the substrate, a protective layer formed on the first cladding layer, a core formed in a groove that penetrates through the protective layer and reaches the first cladding layer, and a second cladding layer formed on the protective layer and the core.