Structure transformations accompanying reoxidation preliminary reduced at 270 degrees C copper chromite were studied using X-ray powder diffraction method, and comparison of the structures of the initial and reoxidized copper chromite was carried out. Conditions under which cation-deficient spinel, stabilized with hydrogen and epitaxially bonded with its surface Cu particles (derived from reduction of copper chromite by hydrogen) forms copper chromite with the tetragonal spinel structure are revealed. It is shown that the reoxidized spinel is non-stoichiometric and possibly contains some amount of hydrogen in the form of protons bonded to the lattice oxygen. Differences of reversible phase transformation of copper chromite under reduction-reoxidation conditions from reversible polymorphism of copper chromite with temperature variations are analyzed.