A three-dimensional sensor optical waveguide which permits size reduction, and a three-dimensional sensor employing the same. A three-dimensional sensor optical waveguide includes a plurality of frame-shaped optical waveguide members stacked coaxially in a thickness direction, and a measurement space defined by inner spaces of the stacked frame-shaped optical waveguide members. The optical waveguide members each include a light emitting core, a light receiving core and an over-cladding layer covering the cores. The light emitting core has a light output end positioned in one of opposed inner edge portions of each of the frame-shaped optical waveguide members. The light receiving core has a light input end positioned in the other inner edge portion of each of the frame-shaped optical waveguide members.