Abstract: Acetylated degraded polysaccharides from Laminaria japonica(ADLP)were prepared by the combination of ultrasonic degradation and acetic anhydride method,and the chemical composition,physicochemical properties,antioxidant activity and absorption/retention activities of polysaccharides were evaluated. The results showed that,the acetic anhydride method had successfully introduced the acetyl group into the degraded polysaccharides from Laminaria japonica(DLP),the dissolving capacity of ADLP was significantly better than that of LP,the relative viscosity of ADLP was significantly lower than that of LP. Its antioxidant activities(DPPH free radical scavenging ability,hydroxyl radical scavenging ability,and total reducing ability)were significantly improved(p<0.05),the total reducing ability of ADLP was 87.99% higher than that of Laminaria japonica polysaccharides(LP),the moisture absorption activities of ADLP were significantly improved,its moisture absorption capacity was increased to 25.4% compared with LP,all polysaccharides showed greater moisture retention activities than glycerol. These results suggested that the combined treatment of degradation and acetylation could significantly enhance the physicochemical properties,in vitro antioxidant activities,and moisture absorption/retention activities of Laminaria japonica polysaccharides.