Casein hydrolysates exert various biological activities,and the responsible functional peptides are being identified from them continuously.In this study,the tryptic casein hydrolysate was fractionated by an ultrafiltration membrane(3 kDa),and the peptides were identified by capillary electrophoresis-quadrupole-time-of-flight-tandem mass spectrometry.Meanwhile,in silico methods were used to analyze the toxicity,solubility,stability,and affinity between the peptides and angiotensin-I-converting enzyme(ACE).Finally,a new angiotensin-I-converting enzyme inhibitory(ACEI)peptide,EKVNELSK,derived from αs1-casein(fragment 35-42)was screened.The half maximal inhibitory concentration value of the peptide is 5.998 mM,which was determined by a high-performance liquid chromatography method.The Lineweaver-Burk plot indicated that this peptide is a mixed-type inhibitor against ACE.Moreover,Discovery Studio 2017 R2 software was adopted to perform molecular docking to propose the potential mechanisms underlying the ACEI activity of the peptide.These results indicated that EKVNELSK is a new ACEI peptide identified from casein hydrolysate.