Angiotensin-I Converting Enzyme (ACE, EC 3.4.15.1) plays an essential role in controlling blood pressure. In this research, ACE inhibitors extracted from Arthrospira platensis thermolysin protease were provided using various chromatographic techniques, including reversed-phase high-performance liquid chromatography (RP-HPLC) and strong cation exchange chromatography (SCX). The amino acid sequence was determined by liquid-chromatography-tandem mass spectrometry (LC-MS/MS) and identified using two independent approaches: database-assisted identification and de novo sequencing. FY11 (FSESSAPEQHY) and IR5 (ILLYR) were established with the m/z 1281.54 and 677.37, respectively. The IC