In this work, the deactivation of a CrOx/Al2O3 dehydrogenation catalyst in an industrial reactor has been systematically studied under cyclic dehydrogenation regeneration conditions from start up to end of run. The results showed that the CrOx/Al2O3 catalyst deactivation occurred through three major processes. The first process is related to the complex transformation of surface chromium species, the second process refers to the phase transformation and/or sintering of support alumina, and the third process is the interfacial CrOx/Al2O3 transformation into the solid solution of alpha-(Al, Cr)(2)O-3. In addition, the reduction of the chromium oxide surface area and the migration of Cr3+ into the alumina support resulted in the increase of the surface Cr6+/Cr3+ ratio at the end of the run which increased the specific catalyst acidity and reduced the catalyst selectivity. The main causes of irreversible deactivation of the CrOx/Al2O3 catalyst are the decrease of chromium oxide surface area, the formation of alpha-(Al, Cr)203 in the support, and the increase of surface Cr6+/Cr3+ ratio.