The separation possibility of a gaseous H2–D2mixture by selective permeation through polymers is studied. For this, the Permeabilities, diffusivities and solubilities of pure H2and D2at 296 K were measured for six polymers sheets. The dependence of permeabilities on temperature was determined in the range of 260–360 K. It Was found that the isotopic effect at permeation is strongly dependent on the nature of the polymer and on the temperature. In the end, the possibility of separating a H2–D2mixture by selective permeation through polymers, Pd and microporous glass is discussed.