Abstract: Ammonium transporters are a kind of active ion carriers existing as a kind of transmembrane protein with proposed molecular weight of about 48 kDa. In the beginning of this article a brief introduction is given to research history of this transporter and its relationship with ammonium excretion, followed by the detailed description of the research progress of both prokaryotic and eukaryoticamtB gene cloning and its expression. Finally, the function of Amt in the ni trogen assimilation and the existence of Amt in all kinds of organisms are summarized.