Zeolite easily exchanges its cation to another. As a result, pore size changes easily. Cation-exchanged mordenite type zeolite (MOR) has been reported to have comparatively good isotope separation capability at temperatures higher than 77K. However, correlations between adsorption capacities, adsorption rate, cation variety, and cation exchange ratio have not been clearly indicated. In this work, the cation (Na + ) of synthetic mordenite type zeolite (Na-MOR) was exchanged by alkaline metal ion or alkaline earth ion (e.g., Li + , K + , Mg 2+ and Ca 2+ ). Then, adsorption capacities of H 2 and D 2 were investigated at 77K, 159K, 175K and 195K. Adsorption capacities on Li-MOR and Ca-MOR became larger than that of Na-MOR at a low-pressure range, while that of K-MOR became smaller. Micro-pore size indicated that only K-MOR was clearly shifting to smaller size. In the case of alkaline metal, cations with lower atomic numbers may lead to increased adsorption capacities.