In addition to [6]-gingerol four new constituents were isolated as potent inhibitors of prostaglandin (PG) biosynthesis from ginger, the roots of Zingiber officinale Roscoe. Their structures were identified as [6]- and [10]-dehydrogingerdione (I and II) and [6]- and [10]-gingerdione (III and IV) by the interpretation of spectral data.