Effects of high-energy particle irradiation on the thermal relaxation of hydrogen disordering in the Pd–H system have been studied at low temperatures. A palladium foil (1.5 μm thick) doped with hydrogen up to the atomic ratio, H/Pd, of about 0.6 is used as a specimen. First, the hydrogen disordering is induced in the PdH 0.6 specimen by the following two means; fast cooling of the specimen from 80 K to 10 K, and irradiation at 10 K with 60 MeV 12 C ions. Then, the thermal relaxation behavior of hydrogen disordering is observed up to 80 K by measuring the electrical resistivity as a function of temperature. From the measurements at several heating rates (1, 2, 5 and 10 K/min), we determine the activation energy of hydrogen migration in the relaxation process to the thermal equilibrium state by means of a cross-cut method. Based on the experimental results, we discuss the difference between relaxation of hydrogen disordering by fast cooling and that by ion irradiation.