A new C₂₀-diterpenoid alkaloid, yesonine (1), a new C₁₉-diterpenoid alkaloid, α-oxobrowniine (2), and five known alkaloids were isolated from Aconitum yesoense var. macroyesoense (Nakai) Tamura. Structures of those new alkaloids were determined on the basis of their spectral and chemical correlation with known alkaloids. Hydrolysis of yesoline (9) and permanganate oxidation of browniine (10) afforded yesonine (1) and α-oxobrowniine (2), respectively.