In the courses of in vitro screening for the angiotensin converting enzyme (ACE) inhibitory activity of the various extracts from medicinal plants, n-BuOH soluble extract of the seeds of Xanthium strumarium was found to exhibit distinctive angiotensin converting enzyme (ACE) inhibitory activity. Bioassay-guided fractionation and purification of the n-BuOH soluble extract of the seeds of Xanthium strumarium afforded a new $xanthiazone-11-{eta}-glucopyranoside$. The ACE activity was significantly inhibited by the addition of a new $xanthiazone-11-{eta}-glucopyranosidein$ a dose-dependent manner of which $IC_{50}$ value was $21.8;{mu}g/ml$.