Abstract: The ultrasound-assisted extraction, resin decolorization process and antioxidant activity of polysaccharides from Mori fructus (MFPs) were investigated in this work. The effects of ultrasonic extraction temperature, solid-liquid ratio, ultrasonic time and ultrasonic power on extraction yield of MFPs were investigated by single factor and orthogonal test. Taking decolorization rate as index, the effects of decolorization time, concentration of polysaccharide solution and decolorization temperature were investigated by single factor and orthogonal test. ABTS assay, DPPH assay, phenanthroline method and pyrogallol autoxidation reaction were used to evaluate the antioxidant activity in vitro. The results showed that the optimal ultrasonic extraction conditions were ultrasonic temperature 50 ℃, solid-liquid ratio 1:30 g/mL, ultrasonic time 70 min and ultrasonic power 500 W. Under these conditions, the extraction yield of MFPs was 4.59%±0.25%. The optimal decolorization conditions were decolorization time 5 h, concentration of MFPs solution 4 mg/mL and decolorization temperature 25 ℃. Under these conditions, the decolorization rate was 62.34%±1.27%. MFPs had strong scavenging ability on ABTS⁺ radical, DPPH radical, hydroxyl radical and superoxide anion radical with half inhibitory concentration (IC₅₀) of 0.14, 0.68, 0.19 and 3.14 mg/mL, respectively.