The optimization, purification, and characterization of exopolysaccharide (EPS) from Climacodon septentrionalis were investigated. The results showed that the optimal incubation time was 8 days for EPS production by C. septentrionalis; maltose and soy extract were the best carbon and nitrogen sources, respectively. One kind of EPS fraction was purified; it had a molecular weight of about 3.4 × 10(5) Da and mainly comprised glucose (98%). The main structure of EPS is α-glucopyranose. In addition, the EPS showed good antioxidant properties in vitro. The thermal stability of EPS also was investigated, and the results suggest that to maintain its bioactivity the processing temperature of EPS should not be more than 200°C. The structural characteristics of EPS, such as molecular weight, functional groups, monosaccharide constituents, and configuration of the glycosidic bond give EPS great potential for application as a natural antioxidant material in health, food, and therapeutics.