Eight new diterpenoid alkaloids, acoseptrine [5] acosepticine [6], 4-anthranoyllapaconidine [7], acoseptridinine [8], acoseptridine [9], acoseptrinine [10], 14-O-methylforesticine [11], and 6-demethyldelphatine [12], have been isolated from the roots of Aconitum septentrionale, along with seven known alkaloids: N-deacetyllappaconitine [1], septentrionine [2], sepaconitine [4], delvestidine [13], anthranoyllycoctonine [14], lapaconidine [15], and lycoctonine [16]. The structures of the new compounds were assigned by comparison of spectroscopic data with those of related known compounds. The structures of compounds 6 and 7 were confirmed by chemical correlation with the known compounds 6-acetylacosepticine and lapaconidine, respectively. All known compounds were identified by comparison of their spectroscopic data and tlc behavior with those of authentic samples. The use of strongly acidic resins leads to a cleavage of the N-acetyl group in the case of lappaconitine.