A surface plasmon optical waveguide includes a lower cladding, a metal thin layer on the lower cladding, low-k dielectric layers spaced apart from each other on one surface of the metal thin layer, and an upper cladding covering the low-k dielectric layers and the metal thin layer uncovered between the low-k dielectric layers. A refractive index of the low-k dielectric layers is less than a refractive index of the lower and upper claddings.