Corn germ meal was hydrolyzed by alkaline protease to prepare ACE inhibitory peptides. Based on the single-factor experiments, the orthogonal experiment was used to optimize enzymatic conditions and the ACE inhibitory rate was used as the indicator. The optimal condition was as follows: substrate concentration was 5% (W/V), enzyme concentration 3% (W/W), temperature 60℃, pH 5.5, hydrolysis time 2.5h. Under the condition the inhibition of the hydrolysate against ACE was the strongest, the inhibitor rate was 86.38% and the degree of hydrolysis was 22.7 6 %. The hydrolysate was separated by the ultrafiltration membrane with the molecular weight cutoff 6 KDa. The inhibitory activities of the two fractions were determined. The 50% inhibitory concentration (IC50) of fraction Ⅱ was 1.38 mg/mL, which was higher than that of the un-ultrafiltration fraction (3.16 mg/mL).