Changes of the V2O5/Al2O3 catalyst aged for up to 10 years under real conditions of the selective catalytic reduction of NOx by ammonia (SCR) at the tail gases of the nitric acid plant were characterized by V-51 NMR spectroscopy, porosimetry, temperature programmed reduction (TPR) and catalytic activity measurements. The catalytic activity and the redox properties of the catalyst were found intact. Only small variations of the ratio of the octahedral and tetrahedral vanadia species were documented by V-51 NMR on aged catalyst.