The separation of a hydrogen isotope mixture on porous materials was studied using equilibrium and breakthrough experiments. The adsorption equilibria of H-2 and D-2 on SBA-15 with mesopores and molecular sieves 5A, Y, and 10X with micropores were measured at 77 K using the volumetric method. The breakthrough experiments of a H-2 and D-2 mixture in each adsorbent bed were carried out at various conditions of flow rate and pressure. The equilibrium ratio of D-2 TO H-2 on mesoporous molecular sieves was larger than the ratio on microporous molecular sieves (SBA-15 > 10X > Y > 5A), but the difference among the adsorbents decreased with increases in pressure. On the other hand, the order of breakthrough separation factor showed the opposite result (SBA-15 < 10X < Y < 5A). The breakthrough separation fact ors for zeolite 10X was approximately equal to the equilibrium ratio of D-2 TO H-2 at the corresponding partial pressures, whereas zeolites 5A and Y showed higher breakthrough separation factors than their equilibrium ratios. In SBA-15, the separation factors from breakthrough results were even smaller than the corresponding equilibrium ratio. In the microporous adsorbent with a limited pore size (zeolite 5A in the study), the diffusion mechanism contributed to the separation of hydrogen isotope gases as one of key factors. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.