The extraction of polysaccharides from Grateloupia livida (GLP)was optimized using one-factor-at-a-time method and response surface methodology.Solid-to-solvent ratio, temperature and time were used as independent variables while polysaccharide yeild was used as response variable.The antioxidant activity of GLP was investigated by measuring scavenging activities against 1,1-diphenyl-2-trinitrophenylhydrazine(DPPH) and hydroxyl radicals(·OH).The results showed that the optimum extraction conditions were found to be extraction at 100℃ for 4 h with a solid-to-solvent ratio of 1:37 g/mL, while polysaccharide yeild was 15.23%. GLP possessed strong antioxidant activity with half inhibitory concentration(IC₅₀) for scavenging of DPPH and hydroxyl radicals. 12.61 mg/mL and 2.05 mg/mL,respectively.