The isotherms of molecular hydrogen isotopes adsorbed in NaA zeolite, measured by microgravimetry from 120 to 77 K, have been approached by the Dubinin model. The adsorbed amounts slightly increase from H2 to D2. This fact is related to the values of the covolumes of the species in the fluid phase. The heats of adsorption are around 10 kJ/mol and decrease with the adsorption amount. From the adsorption entropy we have estimated the external and librational frequencies.