To investigate the activity and structure of angiotensin-converting enzyme (ACE) inhibitory peptides derived from marine collagen oligopeptides (MCOPs), MCOPs were prepared from deep-sea salmon skin by two-step enzymolysis. Based on analysis of the molecular weight distribution, the ACE inhibitory activity of MCOP was determined. The results showed that the components with a molecular weight of less than 1000 u in MCOP accounted for up to 90.79% of all proteins and were mainly distributed in the range of 132~576 u, and the corresponding IC50 for ACE activity was 1.18 ± 0.12 mg/mL. Subsequently, MCOPs were separated and purified by reverse-phase high performance liquid chromatography (RP-HPLC) and the ACE inhibitory activity of 11 fractions was measured. Seven fractions had a higher ACE inhibitory activity than the total MCOP mixture. Finally, structural identification of peptides in the 11 fractions was performed on a quadrupole time-of-flight (Q-TOF) mass spectrometer and the ACE inhibitory activity of the 15 identified peptides was determined. The results indicated that all peptides exhibited ACE inhibitory activity and Ala-Pro (AP), Val-Arg (VR), and Gly-Arg (GR) showed stronger activities than the total MCOP mixture. The IC50 values of the three peptides were 0.07 ± 0.01 mg/mL, 0.35 ± 0.03 mg/mL, and 0.92 ± 0.85 mg/mL, respectively. Their ACE inhibitory activities were 16.86, 3.37, and 1.28 times the inhibitory activity of the MCOP mixture, respectively. Therefore, AP, VR, and GR are peptides with potent ACE inhibitory activity.