Abstract: In this paper, peptide was prepared from Cucumaria frondosa by enzymatic hydrolysis with complex protease, and its composition and antioxidant capacities were evaluated. Taking the degree of hydrolysis as the index, the enzymolysis parameters were optimized by single factor experiments and response surface experiment. The nutrients, amino acid composition, molecular weight distribution and in vitro antioxidant activity of the Cucumaria frondosa peptide were analyzed. The results showed that the optimized conditions were as follows: Material liquid ratio 1:1.5 (w:w), temperature 49 ℃, initial pH7.0, enzyme dosage 1052 U/g and enzymolysis time 4.7 h. Under these conditions, the degree of hydrolysis of Cucumaria frondosa was 30.51%±0.85%. The average relative molecular mass of the Cucumaria frondosa peptide was 403 Da, and the proportion of relative molecular mass less than 1 kDa was 92.81%. The content of total amino acids in peptide was 80.54%, and the proportion of hydrophobic amino acids and the umami acid were 38.00% and 44.10% respectively. So the Cucumaria frondosa peptide had high nutritional value and the characteristics of easy absorption because of its high content of small protein molecules. The antioxidant capacity test showed that the IC₅₀ of the scavenging concentration of hydroxyl radical and superoxide anion were 0.19 and 0.49 mg/mL, respectively. This would provide a theoretical basis for the development and utilization and deep processing of Cucumaria frondosa.