Abstract: Extraction, purification and biological activity of polysaccharide from Glycyrrhiza uralcnsis in Gansu were studied.The optimal ultrasonic-assisted extraction technology of polysaccharide was determined by response surface methodology. The polysaccharide of G. uralensis Fisch. ( GCP2) was obtained by the DEAE-52 anion exchange column chromatography and Sephadex G-100 gel filtration, respectively.The composition and molecular weight of the polysaccharide purified were analyzed by gas chromatography and high performance size exclusion chromatography with multi-angle laser light scattering ( HPSECLLS) .The antioxidant and antibacteria activities of GCP were determined in vitro. Results indicated that the optimal extraction conditions were as follows: extraction temperature 70 ℃, extraction time 85 min, liquid-solid ratio 13 ∶ 1, ultrasonic power600 W. Under the optimal extraction conditions, the extraction rate of polysaccharide was up to 4.23%.GCP2 was obtained by the chromatographic technique, which was a yellow white powder and reducing sugar without starch.GCP2 consists of arabinose, glucose and galactose with the molar ratio of 0.166∶ 5.56∶ 1.60, and had the characteristic of glycoconjugate by infrared spectrum analysis.HPSEC-LLS analysis results showed that the GCP2 was composed of three different components of polymer, average molecular weight of the main components was 1.378 × 10~5g/mol.GCP2 had strong scavenging effect on ·OH free radicals and O₂^-·free radicals with the IC₅₀ of 3.48 mg/m L and 3.43 mg/m L, and had the reductibility increased with the increase of concentration. Antibacteria test showed that GCP2 had better restraining effect on six different bacteria, especially for Escherichia coli and Pneumonia klebsiella strains.