A Y-branched optical waveguide with a uniform output characteristic for use in optical communication systems is disclosed. The optical waveguide, consisting of a core section serving as a transmission medium of an optical signal and a cladding section surrounding the core section, is formed on a semiconductor substrate. An input-tapered waveguide is configured to receive the optical signal through a first ending section and to output the optical signal through a second ending section, with a symmetrical structure with respect to a centered line of the input-tapered waveguide, so that a width of the input-tapered waveguide extends more widely along the centered line. A pair of first and second output-tapered waveguides each are configured to receive the optical signal branched through the second ending section, from which the pair of first and second output-tapered waveguides respectively extend downstream, with an asymmetrical structure with respect to the centered line, a respective width of the first and second output-tapered waveguides extending more widely along the centered line.