Semen Coicis (S. Coicis) has been regarded as a valuable source of traditional herbal medicine in China for thousands of years. S. Coicis polysaccharides (SCPs) are one of the most important bioactive ingredients of S. Coicis, which have attracted worldwide attention, because of their great marketing potential and development prospects. Hot water extraction is currently the most commonly used method to isolate SCPs. The structural characteristics of SCPs have been extensively investigated through various advanced modern analytical techniques to dissect the structure-activity relationships. SCPs are mainly composed of diverse monosaccharides, from which Rha and Ara are the most prevalent glycosyl groups. In addition, the structures of SCPs are found to be closely related to their multiple biological activities, including antioxidant activity, immunomodulatory function, antitumor activity, hypoglycemic effect, intestinal microbiota regulatory activity, anti-inflammatory activity, among others. In view of this, this review aimed to provide systematic and current information on the isolation, structural characteristics, and bioactivities of SCPs to support their future applications as therapeutic agents and functional foods.