PURPOSE: To obtain an optical waveguide of a low loss by having projecting parts to limit a light propagation region on a substrate and providing a core layer and clad layer to the upper part thereof.

CONSTITUTION: The substrate 1' having a flat surface is prepd. and the waveguide part is covered by, for example, a photoresist 5. The part except the waveguide part is etched and thereafter, the resist is removed to form the substrate 1 having the projecting parts which are the optical waveguide part. The clad layer 2, core layer 3 and clad layer 4 are successively deposited on such substrate 1 and the substrate is cut out by which the optical waveguide is obtd. A quartz or silicon substrate is used for the substrate 1. The projecting parts which are the light propagation region are formed on the substrate 1 by cutting the part except the light propagation region to a groove shape by etching or the like. Known methods such as, for example, thermal CVD method and flame hydrolysis deposition method are used as the method for successively depositing the clad layers and core layers on the substrate 1.