This research studied microwave assisted extraction process of germinated brown rice polysaccharides (GBRP). The extraction process was optimized by response surface methodology. Antioxidant activities of the germinated brown rice polysaccharides (GBRP) were also studied. On the basis of single factor experiment, the microwave assisted extraction rate of GBRP from germinated brown rice was optimized by Box-Behnken model. The antioxidant activities of the GBRP (in vitro) were investigated based on reducing force to Fe³⁺, scavenging rate to DPPH·, O-2·, and ·OH, and inhibition to lipid peroxidation five testing factors. The results showed that the optimal conditions were as followed: extraction temperature 40 ℃, microwave power 604 W, ratio of solvent to material 24 mL/g, and microwave time 3.83 min. The optimized extraction conditions led to 2.82% extraction rate of the GBRP. The absorbance of the reducing force to Fe³⁺ of the GBRP was 0.196. The DPPH· scavenging rate of the GBRP reached to a maximum value of 52.71%, resulting half maximum effective concentration (EC₅₀) value 0.34 mg/mL. The clearance rate of O^-₂reached to 40.18%, resulting EC₅₀ value 0.23 mg/mL. The maximum scavenging rate to ·OH was 88.41%, resulting EC₅₀ value 0.211 mg/mL. The scavenging rate is 1.37 times higher than that of Vitamin C (V_C). The maximum value of inhibition to lipid peroxidation was 60.86%, getting EC₅₀ value 0.077 mg/mL. The inhibition ability is 1.5 times stronger than that of Vitamin C. Testing results showed that germinated brown rice polysaccharides (GBRP) possesses relatively strong antioxidant ability (in vitro).