The reduction of NOx in exhaust gas has been a major challenge in diesel engine development. For the NOx reduction issues, a new Lean NOx Catalyst (LNC) aftertreatment system has been developed by Honda. A feature of the LNC system is the method that is used to reduce NOx through an NH₃-Selective Catalytic Reduction (NH₃-SCR). In an LNC system NOx is adsorbed at lean conditions, then converted to NH₃ at rich conditions and subsequently reduced in the next lean phase.In recent years, as the efficiency of the diesel engine has improved, the exhaust gas temperatures have been reduced gradually. Therefore, the aftertreatment system needs to be able to purify NOx at lower temperatures. The development of a new LNC which has a high activity at low temperature has been carried out. For the improvement of the LNC three material improvements were developed. The first of these was the development of a NOx adsorbent which is matching the targeted exhaust gas temperatures. The second improvement was the development of a layer configuration to reduce the negative cross-effects of NOx adsorbent and zeolite at low temperature. The final improvement, the most important and challenging issue, was the improvement of catalyst durability. Furthermore, the improvement of A/F control considering NOx adsorption performance and NH₃-SCR performance was carried out.As a result, a new LNC system which has high performance even in low exhaust gas temperature was established by new technologies applied to the LNC and improved A/F control.