Synthetic zeolite is the candidate material of the separation column of the gas chromatograph for the hydrogen isotope analysis. Mordenite (MOR) is one of the zeolite, and has been reported that the MOR column can separate hydrogen isotope at about 200K. So, the present authors have investigated the adsorption capacities of H2 and D2 on MOR at various temperatures, and have predicted the adsorption isotherms of HD, HT, DT and T2. In this work, the adsorption capacities of tritium on MOR at 77K and 87K were investigated, and they were compared with the predicted isotherms. The observed isotherm at 87K agreed with the predicted isotherm well in low pressure region. However, at 77K, the adsorption capacity at low pressure region was smaller than that of D2.