The electronic and optical properties of siliphene (carbon-substituted silicene) were investigated using density functional theory (DFT) with the combination of Non-Equilibrium Green’s function (NEGF) formalisms. It was found that carbon-substituted silicene has semiconductor behaviour with 2.01 eV band gap when the ratio of carbon:silicon is 1:1. Moreover, by the low energy ranges, for the x, y and z polarizations of the real part of the dielectric function, the optical refraction (n) for the most of the allowed energies is higher than that of the graphene. For the perpendicular to the nano layer plane polarization, the static refractive index of siliphene (C:Si = 1:1) is lower than that of the graphene and silicene as well.