BACKGROUNDLycium ruthenicum Murray (LRM), a perennial shrub plant belonging to the Solanaceae family, is rich in anthocyanins, which have anti‐inflammatory, antioxidant, lipid‐lowering, intestinal flora regulating, and other pharmacological qualities. This study was primarily aimed to investigate the inhibitory effect of different anthocyanin purities from LRM on angiotensin‐I‐converting enzyme (ACE) activity in vitro. Moreover, the inhibitory mechanism was further analyzed by molecular docking technology.RESULTSTwo main anthocyanin isomers were identified by ultra‐performance liquid chromatography–tandem mass spectrometry and proton/carbon‐13 nuclear magnetic resonance, namely petunidin‐3‐O‐[rhamnopyranosyl‐(trans‐p‐coumaroyl)]‐5‐O‐(β‐d‐glucopyranoside) (trans‐Pt3R5G) and petunidin‐3‐O‐[rhamnopyranosyl‐(cis‐p‐coumaroyl)]‐5‐O‐(β‐d‐glucopyranoside) (cis‐Pt3R5G), with a molar ratio of 9:1. Three purification grades of Pt3R5G all showed excellent inhibitory effects on ACE, with the half maximal inhibitory concentration (IC50) values being 0.562, 0.421, and 0.106 mg·mL−1. Increasing the purity may reduce the IC50 within a certain concentration range. An enzymatic kinetic experiment showed that the inhibitory effect of Pt3R5G on ACE was reversible and non‐competitive: Pt3R5G and substrate were not in competition for the active sites of ACE. Molecular docking technology further revealed the possible mechanism was that Pt3R5G and ACE amino acid residues were interacting by hydrogen bonds to exert the inhibitory effect.CONCLUSIONThe results indicated that Pt3R5G from LRM was highly effective at inhibiting ACE activity in vitro, with the hydrogen bonds of Pt3R5G and ACE amino acid residues exerting the inhibition. As a potential plant‐based ACE inhibitor, Pt3R5G can be used as a functional ingredient for antihypertensive effects. © 2023 Society of Chemical Industry.