As the structural characteristics of peptides affect their functional properties, they are an important factor for peptide stability. The stability characteristic was investigated in two groups of synthetic peptides, analogues of VLSTSFPPK (VL-9). The latter was previously purified from Kluyveromyces marxianus protein hydrolysate. In the first group, the replacement impact of Pro in antepenultimate position with Tyr, Cys and His on antioxidant stability against heat, NaCl, and pH and in the second group, the replacement effect of Lys in C-terminal with Trp, Tyr, and Phe on the stability of antihypertensive activity under gastrointestinal digestion were studied. Pro containing peptide (VL-9) showed the highest antioxidant stability against heat and salt. Despite the positive effect of Cys in antioxidant activity of peptides (VCK-9), it decreased the heat and salt stability. Tyr increased the ABTS cation radical scavenging activity and resulting peptide had the same thermal stability as the primary peptide and higher sensitivity to salt. Despite not significant effect of His on the antioxidant activity, it caused a slight instability against heat and salt. The antioxidant peptides studied showed the highest stability at neutral pH. The higher hydrophilicity of Lys in the peptide sequence caused higher ACE-inhibitory stability in simulated GI digestion.