We examined ACE inhibitory activity and the antihypertensive effect of M. citrifolia juice. The juice strongly inhibited ACE activity. The inhibitory effect of juice from ripe fruit is stronger than that of green fruit. Furthermore single oral administration of the juice reduced systolic blood pressure of male spontaneously hypertensive rats. These results indicate that the juice contains ACE inhibitory compounds, and daily intake of the juice is effective for prevention and improvement against hypertension.