Mechanical properties of the Nb2C and U(N,C) inclusions and matrix in the U-5.5Nb alloy are characterized by nanoindentation and the yield strength and plasticity index are calculated from the obtained hardness. The result from experiment shows that the Nb2C inclusion has the highest elastic modulus and hardness, while the corresponding values of the U(N,C) inclusion are far less than those in the Nb2C inclusion but higher than matrix. Moreover, the result calculated from hardness shows that the yield strength of the Nb2C inclusion is the highest, but the plasticity index is the lowest, which reveals that the Nb2C inclusion inclines to elastic deformation. However, the yield strength of the U(N,C) inclusion is low and the plasticity index of the U(N,C) is the highest, which reveals that the U(N,C) inclusion prefers to plastic deformation and also can broke easily. Elastic modulus and hardness from multi-cycle load/unload test are close to those obtained by single load/unload test, in addition, the elastic modulus obtained from nanoindentation is accord to the value obtained by tensile test in the literature.