Selenium polysaccharides (Se polysaccharides) are a kind of organic selenium compounds which obtain the activities from Se and polysaccharides. Comparing to Se or polysaccharides, Se polysaccharides exhibit improved biological activities and are more prone to be absorbed by human bodies, therefore, they have been widely used in medical applications, such as immunomodulation, anti-tumor, anti-oxidation, anti-aging. Due to their unique pharmacological activities, Se polysaccharides from medicinal plants have gradually become a research hotspot. However, only a few of Se polysaccharides have been separated and purified in recent years. The structure of polysaccharides is also very complex, therefore, determination of the chemical structure and mechanism of bioactivity of Se polysaccharide in vivo remain to be further studied. This article systematically introduced the main source and biological activities of Se polysaccharides from medicinal plants. The purpose of this review is to provide a basis for the further research of Se polysaccharides.