Abstract: Lentinan, isolated from the fruiting bodies of Lentinula edodes, was usually extracted with hot water. Lentinan has different composition and M_w according to different samples, and their linkage structure of intramolecular chemical bonds are also different. Lentinan has many biological activities including antitumor, anti-oxidation, immunity enhancement, anti-radiation and anti-side effects and so on, and which could be affected by several factors such as molecular weight, glycosidic bond, higher structure, endogenous metal ions, temperature, ultrasonic treatment, organic reagents and alkali liquor, etc. This review introduces hot water extraction of lentinan and several assistant extraction methods in relation to enzyme, ultrasonic, microwave, high pressure and combination of different methods, and also compares their advantages and disadvantages. Then, the separation and purification of lentinan were also introduced. In this review, the monosaccharide composition of lentinan was explained, various possible primary structures of lentinan were summarized and listed, the triple helix structure and its verification method of lentinan were analysed, and the biological activities of lentinan and their mechanisms were discussed. Next, the internal and external factors affecting the structure and activity of lentinan were summarized. In the end, the future research trend was pointed out about lentinan study.