The structural defects, quenching defects and electron-irradiation defects in the in-termetallic compounds NiAl have been studies with the positron annihilation technique. The recovery behaviour of quenching defects and irradiation defects have been inversti-gated. Two distinct recovery stages have been, found, one at about 280℃ and the other at about 500℃. The experimental results show that the low-temperature stage is due to the annealing out of the divacancies and the high-temperature stage is due to the annealing out of the vacancies; and the density of the conduction electrons at the vacancies and the lattice interstitial sites are nearly equal to each other, but the momentum of the conduction electrons at the vacancies is lower than that at the latties interstitialsites in NiAl.