The structure and properties of pepsin were summarized in this study. The enzyme system compositions of mammal and fish were concluded and the differences in these pepsins were presented. In addition, the newly founded activities of pepsin including digestion of guar galactomannan and nucleic acids were illustrated in details. As pepsin is the main digestive enzyme, the founding that pepsin is a "multifunctional enzyme". Based on the above, some suggestions were proposed for the future study and application of pepsins.