The crystallographic and kinetic aspects of the solid state reaction of ammonium nitrate and copper oxide were studied by in situ time- and temperature-resolved X-ray diffractometry. The reaction proceeds through an intermediate stage in the form of a solid solution of diamminecopper(II) complex in the ammonium nitrate lattice, subsequently resulting in the formation of diamminecopper(II) dinitrate. The kinetic profiles of the reaction were fitted by a nucleation and growth model. The rate of the reaction was found to increase as the dopant concentration decreased. The reaction takes place with an expansion of the tetragonal lattice of the ammonium nitrate along the base, resulting in a plausible pseudo tetragonal-like structure.