Mori Fructus (MF) is the dried fruit of Morus alba L., which is a dual-purpose resource for medicine and food. As one of the main active components of MF, polysaccharides exhibit many biological activities such as immunomodulation, hypoglycaemia effects, liver protection, and regulation of the intestinal flora. In recent years, the extraction and purification methods, structure, biological activity, and structure-activity relationship of Mori Fructus polysaccharides (MFP) have attracted extensive attention. MFP composed of repetitive disaccharide fragments of 1,4-linked α-GalpA and 1,2-linked α-Rhap. Structural information such as extraction yield, molecular weight (Mw), and monosaccharide composition of MFP differs based on the extraction process used. In addition, the Mw, monosaccharide composition, and chemical modification of MFP are closely related to its biological activity. Currently, the research of MFP is still in the primary stage, and further exploration is required to fully reveal their structure and biological functions. This paper systematically reviews the research progress of extraction, purification, structural characterization, and biological activities of MFP, deeply analyzes their structure-activity relationship and product application status, and discusses some existing problems in order to provide support for the further development and utilization of MFP.