Abstract: Objective: The aim of this study was to enhance the polysaccharide yield from Stellariae Radix and evaluate its in vitro antioxidant activity. Methods: Ultrasonic-assisted extraction method was employed to extract polysaccharides from Stellariae Radix, the single-factor experiment was combined with the Box-Behnken response surface to optimize the parameters of the extraction process. Additionally, Sevag method was utilized for the removal of protein to obtain crude polysaccharide of Stellariae Radix, which was further analyzed for its antioxidant activity. Results: The optimized conditions for extracting polysaccharides from Stellariae Radix were an ultrasonic temperature of 50 ℃, a time of 3.20 h, and an extraction frequency of 2 times, resulting in a yield of 28.24%±0.10%. The content of polysaccharide was 59.13%. Notably, the crude polysaccharide demonstrated antioxidant activity with IC₅₀ values of 5.47, 2.40 and 1.44 mg/mL for DPPH, OH, and ABTS⁺ radical scavenging activities, respectively. Conclusion: The optimized extraction process of polysaccharides from Stellariae Radix is feasible and can provide a theoretical foundation for the development and utilization of Stellariae Radix.