Even though substantial improvements have been made for the lean NOx trap (LNT) catalyst in recent years, the durability still remains problematic because of the sulfur poisoning and sintering of the precious metals at high operating temperatures. Hence, commercial LNT catalysts were aged and tested in order to investigate their performance and activity degradation with respect to the fresh catalyst, and establish a proper correlation between the aging methods used. The target of this study is to provide useful information for regeneration strategies and optimize the catalyst management for better performance and durability. With this goal in mind, two different aging procedures were implemented in this investigation. A catalyst was field-aged in the vehicle chassis dynamometer for 100.000 km, thus exposed to real conditions. Whereas, an accelerated aging method was used by subjecting a fresh LNT catalyst at 800 °C for 24 hours in an oven under controlled conditions. Engine dynamometer studies were performed with a Volvo mid-sized diesel engine with the purpose of testing the NOx storage and reduction performance, as well as the THC and CO conversion activity of the catalysts under controlled conditions. The aged catalysts activity was shown to be significantly degraded, mainly at low working temperatures compared to the fresh LNT, due to a limited NO oxidation. On top of that, several vehicle emission cycles were carried out in the vehicle chassis dynamometer with a 2.0 l Volvo XC90 diesel vehicle in order to study the catalysts performance and monitor the gradual deterioration of the field-aged catalyst during the vehicle aging testing.