Abstract: Enzyme-assisted ultrasonic extraction was employed to extract polysaccharides from white lilacs. The effects of various experimental conditions on the yield of polysaccharides from white lilacs were systematically analyzed using the response surface methodology (RSM). The crude extract was purified through DEAE-52 cellulose column and Sephadex G-100 gel column chromatography. High-performance gel permeation chromatography (HPGPC), ion chromatography (IC), ultraviolet spectrum analysis, Fourier infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were utilized for characterization of the polysaccharide structure and its antioxidant activity in vitro was investigated. The results demonstrated that the optimal extraction process for polysaccharides from white lilacs involved ultrasonic power 150 W, ultrasonic time 40 min, ultrasonic temperature 40 ℃, enzyme dosage 2.2%, solid-liquid ratio 1:40 g/mL. Under these conditions, the yield of polysaccharides was 3.03%±0.09%. The polysaccharides were purified using a DEAE-52 cellulose column, and the main component SP-c was collected. Subsequently, SP-c-1 was obtained through a Sephadex G-100 gel column. The monosaccharide composition and molar ratio of SP-c-1 were galacturonic acid, arabinose, galactose, rhamnose, glucose, glucuronic acid, xylose=18.39:11.13:8.96:2.61:1:0.83:0.57, respectively. The weight-average molecular weight (Mw) of SP-c-1 was 14069 Da, and the numerical mean molecular weight (Mn) was 13637 Da. SP-c-1 had the characteristic absorption peak of polysaccharide and contained D-grape pyranose configuration. The half-inhibitory concentration (IC₅₀) of SP-c-1 on DPPH and ABTS⁺ free radicals was 0.87 and 1.355 mg/mL, respectively. Overall results indicate that SP-c-1 exhibits significant antioxidant activity.