Commercial lean NOx trap (LNT) catalysts were aged and characterized to elucidate the effect of aging on their performances and examine the deactivation of a rapid-aged catalyst toward an improved correlation with respect to a vehicle-aged catalyst. Detailed characterization studies were carried out on the flow reactor with small cylindrical cores extracted from the commercial LNT catalysts. Physicochemical characterization techniques were also implemented. The catalyst evaluation revealed that aging resulted in a significant deterioration of NOx storage and reduction functions as a consequence of precious metal sintering, loss of surface area of the NOx storage and support materials, phase transitions of the adsorber compounds, and large accumulation of poison species. Among the aged samples examined, the middle (lengthwise) vehicle-aged sample showed the highest NOx conversion, while the oven-aged catalyst was the most active of the aged samples for water gas shift reaction and oxygen storage.