Abstract: Based on the quantitative structure- activity relationship and predictive models of angiotensin I-converting enzyme (ACE) inhibitory peptide, hydrophobic amino acid residues at C-terminal are positively correlated with ACE inhibitory activity. In order to get more proline and hydrophobic amino acid residues at C terminal, α-chymotrypsin and proline protease were chosen to hydrolyse the shrimp byproducts to produce ACE inhibitory peptides. The hydrolysis times were optimized according to the hydrolysis degree (HD) for α-chymotrypsin, and both HD and ACE-inhibitory activity for proline protease, the results showed that the optimal hydrolysis time for both enzyme were 4 hours. The half maximal inhibitory concentration (IC50) for ACE inhibition of hydrolysate was 1.645mg protein/mL. The hydrolysate was separated into fraction 1 (0⁵00u) and fraction 2 (500¹000u) by molecular weight cut-off (MWCO) membrane. The IC50value of fraction 1 and fraction 2 were 0.333mg peptide/mL and 1.320mg peptide/mL, respectively. The peptide mixtures were analyzed by time-of-flight mass spectrometry. Ten peptides, which were consisted of peptides with 5 to 14 amino acid residues, were identified in fraction 1. Fifteen peptides, which were consisted of peptides with 7 to 14 amino acid residues were identified in fraction 2. The C-terminal amino acids of 22 out of the 25 peptides were proline or aromatic amino acid, which was corresponding to QSAR results.