Angiotensin I converting enzyme (ACE) inhibitory peptides were produced from salmon byproduct proteins via enzymatic hydrolysis using Alcalase, flavourzyme, neutrase, pepsin, protamex and trypsin. Among them, Alcalase hydrolysate showed the highest ACE inhibitory activity, thus ACE inhibitory peptides were purified using consecutive chromatography. The purified ACE inhibitory peptides were identified to be Val-Trp-Asp-Pro-Pro-Lys-Phe-Asp (P1), Phe-Glu-Asp-Tyr-Val-Pro-Leu-Ser-Cys-Phe (P2), and Phe-Asn-Val-Pro-Leu-Tyr-Glu (P4) by time of flight-mass spectrometry/mass spectrometry (TOF-MS) analysis. The IC50 values against ACE activity were 9.10 mu M (P1), 10.77 mu M (P2) and 7.72 mu M (P4). The inhibition mode of P1, P2 and P4 was analyzed using the Lineweaver-Burk plots, demonstrating P1 to be a non-competitive inhibitor, P2 and P4 having a mixed inhibition mode. Taken together, the salmon byproduct protein hydrolysate and/or its active peptides can be used in foods for its benefits against hypertension and related diseases. (C) 2012 Elsevier Ltd. All rights reserved.