Boron was implanted into the p-type Hg0.7Cd0.3Te epitaxial crystals. The implantation was carried out using a fluence of 1.45×1015 cm−2 and an energy of 100 keV. The implanted specimens, as well as unimplanted ones, were annealed without encapsulation by one-zone annealing in an atmosphere of mercury vapor supplied from liquid mercury at temperatures from 250–500 °C. From the annealing of unimplanted specimens, a p-n transition at 350 °C is observed. On the other hand, from the annealing of implanted specimens, it is found that the n-type conductivity induced by implantation damage is gradually reduced with the increase of annealing temperature until a minimum appears around 350 °C, and then increases again. An enhancement of n-type conductivity can be further observed from annealing under a reduced pressure of mercury. A similar result is also obtained from the annealing of implanted specimens using a HgTe compound as the mercury reservoir instead of liquid mercury. The results suggest that the implanted borons become activated dopants after annealing at high temperature. A mechanism on the activation of boron in HgCdTe is thus proposed, and the experimental results can be satisfactorily explained by the mechanism. Journal of Applied Physics is copyrighted by The American Institute of Physics.