Abstract: Angiotensin converting enzyme (ACE) is an important factor causing hypertension. It is urgent to develop a safe and effective ACE inhibitor.The preparation of ACE inhibitory peptide from maize germ protein was optimized by single factor and response surface tests.The effects of enzyme species, enzymatic hydrolysis time, substrate concentration, pH value, enzyme dosage,and temperature on hydrolysis degree and ACE inhibitory activity of hydrolyzed products were studied, and the flavoring enzyme was selected as the enzyme for subsequent experiments. On the basis of single-factor test, Box-Benhnken principle was used to conduct three-factor and three-level response surface test.The results showed that the effects of various factors on ACE inhibition rate were in this order: pH> temperature > enzyme dosage, and the optimal parameters were as follows: pH 6, temperature 40 ℃, and enzyme dosage 13 300 U/g.After practical verification, the optimum enzymatic hydrolysis conditions were determined as follows: substrate concentration 3%, enzymatic hydrolysis time 120 min, pH 6, temperature 40 ℃, and enzymatic dosage 13 300 U/g. Under this condition, ACE inhibition rate reached (85.64±0.98)%, which was close to the predicted value.The ACE inhibitory peptides of maize germ protein has the dual characteristics of functional factor and natural food. This study will provide a theoretical basis for the development of antihypertensive drugs and related functional food.