Cholecystokiniu is a peptide, which distributed widely throughout the gastrointestinal tract and the central nervous system, and has a number of physiological effects. In addition to gallbladder contraction, cholecystokinin also regulates enzyme secretion and growth of pancreas, intestinal motility, satiety signalling and the inhibition of gastric acid secretion. Cholecystokinin is a transmitter in central and intestinal neurons and is also the most abundant neuropeptide. In this paper, the function of Cholecystokinin was reviewed.