Investigation of the constituents of Eurycoma longifolia Jack, obtained from several regions of Viet Nam, has resulted in the isolation of two steroids, namely β-sitosterol and campesterol, 2,6-dimethoxybenzoquinone, and a bitter principle called eurycomalactone (la). Eurycomalactone is closely related to the other bitter principles previously encountered in the family Simaroubaceae. Eurycomalactone is the first compound of this series with a keto group at C-6 and a γ-lactone group between positions 14 and 7. The configuration is discussed. Dihydroeurycomalactone (Za) is also isolated from the bark of Eurycoma longifolia originated from Dinh-Quan.