Disclosed herein is a cantilever-type PLC optical attenuator. The optical attenuator includes a base substrate made of silicon, an input waveguide, and output waveguide. Front portions of the upper and lower silicon substrates around the output waveguide are thinner than rear portions of the upper and lower silicon substrates around the output waveguide to provide a cantilever part having upper and lower cantilever substrate parts. A first electrode is provided on a bottom of the lower cantilever substrate part, and a second electrode is provided on the base substrate to electromagnetically correspond to the first electrode. When a voltage is applied between the first and second electrodes, the cantilever part moves up and down by an electromagnetic force, thus controlling the output light.