A new diterpenoid alkaloid, 2-acetylseptentriosine 121 (2a-acetoxyhetisanelg,9/3,19t~-triol), has been isolated from the roots of Aronitum septentrionale, and its structure established by correlation studies and a single crystal X-ray structure determination.Isolation and structure determination of norditerpenoid alkaloids, 6-0 acetylacosepticine, N-acetylsepaconitine, acoseptrigine, acoseptriginine, Ndeacetyllappaconitine, lapaconidine, lappaconine, lappaconitine, lycoctonine, 8-0- methyllycaconitine, puberaconit ine, septentridine, and septentrionine, from the roots of Aconitum septentrionale Koelle (Ranunculaceae) has been reported earlier (14). Further, the structure elucidation of the diterpenoid alkaloid septentriosine 117 was recently described by us (5). In this communication, we report the isolation and structure determination of 2-acetylseptentriosine 127 obtained in 0.04% yield from the roots of A. septentrionale.