Abstract: The nucleation and growth of hydride on U-2.5Nb alloy was characterized utilizing a Sievert’s-type apparatus with an optical microscope, and the kinetics of hydriding was calculated from the measured decreases in pressure. The effect of temperature and pressure and oxide thickness on the behavior of hydriding was studied. The hydriding rate of U-2.5Nb alloy is higher much than that of U. Hydriding induction time decreases as the temperature increases, which follows the Arrhenius law under a temperature of about 125 ℃, but beyond 125 ℃, induction time increases sharply with temperature increasing. Induction time varies as the inverse of the hydrogen pressure, which follows the reciprocal relation. The oxide thickness on U-2.5Nb surface affects the induction time clealy, and induction time increases with the increasing of oxide thickness.In the case of hydriding with long induction time, reaction site is fewer, and nucleation distribution is asymmetrical that is apt to local corrossion.