Abstract: The reaction kinetics of uranium and uranium-niobium with hydrogen gas is studied by pressure-volume-temperature (P-V-T) method. The results show that preheating and annealing can shorten the incubation period for the reactions of bulk uranium and uranium-niobium alloys with H_2. The influence of preheating in the temperature range 600～700 ℃ on the hydrogenation kinetics is different for uranium and uranium-niobium alloys. When samples are preheated at 600 ℃, cooled down to 200 ℃, and then let to react with H_2 at this temperature, the reactivity increases along the sequence low-carbon uranium < high-carbon uranium < 93% U-7% Nb alloy < 96.5% U-3.5% Nb alloy.