Nitrite oxidoreductase (NXR) is the key enzyme responsible for the oxidation of NO2- to NO3- in nitrite-oxidizing bacteria. Since NXR is a dissoluble enzyme, located at the inner side of the membranes of cells, its function is dependent on the electron transfer chain related to membranes. This paper reviews the advances in study on NXR, including the structure, catalysis mechanism and the impact of different factors. New techniques applied in recent studies and research prospects are also presented.