In nowadays, reducing emissions of the nitrogen oxide (NOx) in diesel engines become a principal goal for the future. The new technology Lean NOx Trap (LNT, is also known like NOx adsorber catalyst (NAC) or NOx Storage and Reduction (NSR) catalyst) can be applied on passenger cars, light and heavy-duty diesel engines to reduce NOx emissions substantially. The NOx emissions are absorbed onto a catalyst during lean engine operation. After the catalyst is saturated, the system is regenerated in short periods of fuel rich operation during which NOx is catalytically reduced. This paper presents a literature review about the function and importance of LNT as the new aftertreatment exhaust system for reducing the NOx emissions of the new generation of diesel engines.