Two new 1,2-seco-1-nor-6((5 $\mapsto$ 수식 이미지 10)abeo-picrasan-2,5-olideskeleton quassinoids, eurylactones A [1] and B [2], and two new $C_{19}$ skeleton quassinoids 3 and 4 were isolated from Eurycoma longifolia together with two known $C_{18}$ quassinoids 5 and 6. Their sttuctures were established by the spectral evidence.Many quassinoids have already been isolated (1-3) from the roots, wood, and leaves of Eurycoma longiolia Jack (Simaroubaceae) and have been used as a folk medicine insoutheast Asia. As part of a series of studies, we have further undertaken the chemicalinvestigation of the n-BuOH-soluble fraction of the MeOH extract and isolated two new1,2-seco-1-nor-6(5 $\mapsto$ 수식 이미지 10)abeo-picrasane skeleton quassinoids 1 and 2, which have beenknown only in shinjulactone B (4,5) and yadanfiolide (6), two new $C_{19}$ 수식 이미지-type quasslnolds3 and 4, and two known C18-type quassinoids 5 and 6. In this paper, the structureelucidation and biosenetic relation of these compounds are described.