Cryogenic adsorption is effective for the recovery of low-concentration hydrogen isotopes in bulk helium gases. In a fusion power plant, application of this process is foreseen for the recovery of tritium from the blanket sweep gas and cleanup of the helium discharge exhaust gas. The authors performed a screening test to find more suitable adsorbents for the recovery of hydrogen isotopes from the bulk helium gas at liquid nitrogen temperature. The screening test indicated that a natural mordenite adsorbent has a quite high adsorption capacity for hydrogen under a helium atmosphere. For the adsorption of deuterium, it was found that the natural mordenite adsorbent possesses a high adsorption capacity even at the lower pressure range of hydrogen and deuterium. The adsorption rates of hydrogen and deuterium were quantified by analyzing breakthrough curves obtained in experiments. Evaluated effective pore diffusivities of hydrogen isotopes in the mordenite adsorbents are considerably higher than those in MS5A adsorbents. Thus, it can be said that the natural mordenite adsorbents are suitable for adsorption of hydrogen isotopes from the viewpoint of adsorption rates, as well. The results suggest that mordenite-type adsorbents are promising for the recovery of low-concentration hydrogen isotopes from the helium bulk gas.