Some optical properties of neutron diffusion waves are discussed. Expressions are given for the change in the direction of propagation of the wave components reflected and refracted at the interface between two semi-infinite media by using appropriate formulae for the refraction of the electromagnetic waves in conducting media. It was found that the phase speed of the refracted asymptotic wave depends upon the direction of propagation. This dependence is especially noticeable in graphite/light-water systems. The phase speed is practically constant in graphite/ heavy-water systems. The results predict the existence of the total reflection of the asymptotic wave on the graphite/vacuum interface, providing the incidence angle is larger than ∼23°. Experimental verification of the diffusion wave refraction is suggested.