Abstract: To utilize the protein resources of Penaeus vannamei by-products in a high-quality way, the enzymatic hydrolysis process of the by-product mainly shrimp heads and shells of Penaeus vannamei, was optimized by single-factor and response surface methodology enzymes using proteolytic degree as evaluation indicator. The molecular weight distribution range of shrimp peptides was detected and the antioxidant capacity and immune regulation activity evaluated. Results showed that Alkaline protease has a good synergistic effect with the endogenous enzymes in shrimp head and the optimized enzymatic process parameters were 4% of enzyme addition, 6.5 h of enzymatic digestion time, 40 ℃ of enzymatic digestion temperature and 1∶5 of feed-to-liquid ratio. The molecular mass of shrimp peptide was mainly distributed in range of 75~1 355 Da, accounting for 76.35% detected by gel chromato- graphy. The shrimp peptide had good scavenging activities on hydroxyl radical and 2,2-diphenyl-l-picrylhydrazyl (DPPH) with IC₅₀ values of 4.64 and 3.08 mg/mL, respectively. In addition, at dose of 10 mg/kg, shrimp peptide can significantly promote the proliferation of lymphocytes and improve the immune organ index and phagocytosis index of the immunocompromised model mice, exhibiting a significant immunomodulatory effect.