NO_x is one of the main pollutants in diesel vehicle emissions. Selective catalytic reduction of NO_x by ammonia (NH₃-SCR) has been extensively studied for the lean NO_x control due to its high performance and economic efficiency. Copper based zeolites have been widely used as the De-NO_x catalysts and significant research efforts have concentrated on developing different types of zeolites to improve the activity and durability. Recently, SCR catalysts based on small-pore molecular sieves have been reported for NH₃-SCR with much improved activities and high thermal durability and have received substantial attention. This review sums up the research progress related with Cu-based small pore molecular sieves, such as Cu-SSZ-13 and Cu-SAPO-34, as diesel De-NO_x Catalysts with outstanding low temperature NH₃-SCR activity and hydrothermal stability. The nature of the copper species and the surface acidity are the most important factors that affect the NH₃-SCR performance. Important results on the active sites and catalytic mechanisms are especially discussed in details. The possible developing orientations and research interests on the novel catalysts design and mechanisms of poisoning resistance are previewed.