Phoenixin (PNX) is a newly discovered endogenous neuropeptide produced from small integral membrane protein 20 (Smim20). The most common isoforms are PNX-14 and PNX-20 amino acid peptides. PNX, a ligand of G protein-coupled receptor 173 (GPR173), has been isolated mainly from brain regions such as the hypothalamus and pituitary gland, and from many peripheral tissues. PNX plays an important role in the regulation of reproductive function by increasing the level of gonadotropin-releasing hormone and stimulating the release of luteinizing hormone from the pituitary cells. However, PNX not only regulates the reproductive system, but also exerts anxiolytic, anti-inflammatory and cell-protective effects. In addition, it has many functions in the regulation of behavior, food intake, sensory perception, memory, body fluid balance, cardiovascular functions and energy metabolism. This review will help us to understand the molecular structure of PNX, its physiological effects and functions, and its role in the pathogenesis and treatment processes of various diseases.