Disclosed is an optical waveguide exhibiting excellent optical characteristics over the entire working temperature range, wherein the temperature dependence of refractive index difference between a core resin and a cladding resin is small. Specifically disclosed is an optical waveguide comprising a resin cured product containing a first fluorine-containing monomer having a perfluoroadamantane structure. Consequently, there can be obtained an optical waveguide which is good in both optical characteristics and temperature dependence of refractive index difference between a core resin and a cladding resin.