Eight compounds were isolated from methanol extract of Plantago major L. leaves and investigated for their ability to inhibit angiotensin I-converting enzyme activity. Among them, compound 1 showed the most potent inhibition with rate of $28.06{pm}0.21%$ at a concentration of $100{mu}M$. Compounds 2 and 8 exhibited weak activities. These results suggest that compound 1 might contribute to the ability of P. major to inhibit the activity of angiotensin I- converting enzyme.