Abstract: Selenylation modification of polysaccharides from the extract residue of Sarcandra glabra(Thunb. )Nakai was operated with sodium selenite as modification agent and barium chloride as the catalyst. The synthesis conditions were optimized by orthogonal experiment with the yields and contents of selenium as indicators. Then, the purity, molecular weight, infrared spectroscopy, thermophysical properties and antitumor activity of the selenylated polysaccharides were determined. Results showed that the optimum conditions for preparing selenylated polysaccharides from the extract residue of S. glabra(Thunb. )Nakai were at 70 °C for 7 h with 1. 0% nitric acid using 1. 5 g barium chloride as catalyst. Under the optimum condition, the physicochemical properties of the derivatives were measured and the results showed that the total carbohydrate content was(94. 89±0. 83)%, the yield was(21. 93±0. 85)%, the content of selenium was(944. 54±13. 91)μg/g, the molecular weight was 1 339 kD. In vitro antitumor activity indicated that exposure of HepG2 cells to the increasing concentrations of the crude polysaccharide from the residue of S. glabra(Thunb. )Nakai and its selenylated products decreased cell viability in dose-dependent and time-dependent manner. The selenium polysaccharide demonstrated a better antitumor activity compared with the raw polysaccharide, which could be explored as a potential antitumor drug from abandoned extracted residue for the functional foods and pharmaceutical industries.