Abstract: As a part of the program to develop metal hydride technology for storing and processing tritium,the tritium absorption-desorption of LaNi_(4.25)Al_(0.75) was investigated.The pressure-composition-temperature(P-C-T) and activation characteristics and the absorption-desorption rate of tritium from LaNi_(4.25)Al_(0.75)T_(x) at different temperature were measured.And relative partial molar enthalpy variation ΔH~() and entropy variation ΔS~() for T_(2) absorption and desorption were calculated from the Van't Hoff plots based on the measured P-C-T relations.The calculated values of ΔH~() and ΔS~() during the formation of the LaNi_(4.25)Al_(0.75)T_(2.5) phase are(-31.8±0.8) kJ·mol~(-1)and(-76.5±2.4) J·mol~(-1)·K~(-1),respectively,and the values of desorption are(-36.5±0.5) kJ·mol~(-1)and((-84.2±1.5)) J·mol~(-1)·K~(-1),respectively.Variations in the origin gas tritium and tritium released from 7-day-aged LaNi_(4.25)Al_(0.75) tritide are analyzed by quadrupole mass spectrometer.