Abstract: By comparison of DPPH radical scavenging ability of the Porphyra yezoensis extract with hydrochloric acid, citric acid, acetic acid, sodium carbonate and water solution, the best extraction medium was screened. By single factor experiments and response surface experiment, the optimum extraction conditions were determined. Main components and stability of the extract were also studied. Results showed that the Porphyra yezoensis extracts with hydrochloric acid solution had the strongest DPPH radical scavenging ability and the highest solids content. Optimum extraction conditions were to extract in 0.78mol/L hydrochloric acid solution at 60℃ for 1.5h, with the solid-liquid ratio of 1∶30. There were 54.33% total sugar, 28.22% protein and 13.53% inorganic salts in the the extract. The reducing capacity of the extract was strong and the IC50 of DPPH radical scavenging ability was 0.537mg/mL. The pH value had the greatest impact on stability of the extract, followed by temperature, with light and the metal ions less impact.