Abstract: Since water is a perfect medium for both bacteria and parasitic microbes, fish skin is constantly exposed to pathogen attacks. It is generally believed that skin mucus serves a mechanical as well as biochemical barrier. Lectins, an important part of the mucus, are carbohydrate-binding proteins that are neither antibodies nor enzymes, yet play important roles in innate and adaptive immunity. Based on the structure of the carbohydrate recognition domain (CRD) and their function, fish mucus lectins are classified as four types. Recent research has shed light on the structural diversity and functions in innate immunity of mucus lectins. Here, we reviewed recent research progress on the classification, biological properties and functions of fish mucus lectins. Analyses on other fish species are therefore important in clarifying lectin diversity and their functions in skin mucus.