ABSTRACT: Amaranth seeds have been considered as an excellent alternative or complementary source of food protein due to their balanced amino acid composition. However, their potential as a source of bioactive peptides has not been explored. The present study is aimed at characterizing and evaluating the activity of the angiotensin converting enzyme inhibitor of the amaranth protein concentrate and of hydrolysates produced with Alcalase. The protein concentrate, after simulated gastrointestinal digestion, showed lower angiotensin converting enzyme-inhibitory activity (IC50 of 0.439 ± 0.018 mg protein/mL and 0.475 ± 0.021 mg protein/mL, for untreated and heat treated protein concentrate, respectively) than the hydrolysates produced with Alcalase, before and after simulated gastrointestinal digestion (IC50 0.118 ± 0.009, 0.123 ± 0.007, 0.137 ± 0.002, and 0.176 ± 0.014 mg protein/mL, respectively). The simulated gastrointestinal digestion (pepsin–pancreatin) did not significantly alter the angiotensin-converting enzyme inhibiting activity of the Alcalase hydrolysates, suggesting that the peptides of the hydrolysates were resistant to gastrointestinal hydrolysis. These results highlight the angiotensin converting enzyme-inhibitory potential of amaranth proteins, which is an indication of their health-promoting potential.