Using either single H2 and D2 or H2-D2 mixed gases, the sorption abilities of CHA (chabazite)-type zeolites ion-exchanged with K, Na, or Ca were studied at 77, 201, and 250 K. The LTA (Linde Type A) (3A) and FAU (faujasite)-type zeolites were also examined for comparison. The pore diameters in these materials were found to decrease on the order of FAU > Ca-CHA > [K-CHA, Na-CHA, and LTA(3A)]. The quantities of D2 adsorbed on these zeolites were larger than the amounts of H2. At higher temperatures, the CHA-type zeolites having smaller pores exhibited superior D2/H2 selectivity compared with the LTA(3A) and FAU, suggesting that hydrogen isotope separation using zeolites is affected by pore size.