Abstract: Serine proteinase, purified from the hepatopancreas of Pacific white shrimp (Litopenaeus vannamei), was used to hydrolyze acid solubilized collagen (ASC) isolated from Nile tilapia (Oreochromis sp.) skin to produce angiotensin I-converting enzyme (ACE) inhibitory peptides (ACEIPs). A series of column chromatography assays were used to separate the ACEIPs. A peptide, NPARTCR, was isolated as it exhibited high ACE inhibition potential. Further digestion of this peptide by a proline specific endopeptidase (PSEP), produced a pentapeptide ARTCR with ACE inhibitory activity (IC₅₀) of 77.0 μmol/L. Both NPARTCR and ARTCR inhibited ACE in a non-competitive manner. An in vivo study in rats demonstrated that ARTCR has ACE inhibitory activity via lowering systolic blood pressure in spontaneously hypertensive rats (SHRs). These results suggest that processing by-products from shrimp and tilapia are ideal raw materials for the production of serine proteinase and collagen, respectively. Serine proteinase and collagen are both ideal raw materials that can be used to derive ACE inhibitory active peptides against hypertension.