From the roots of Aconitum crassicaule, two new diterpenoid alkaloids, crassicaulisine and crassicaulidine, were isolated. The structure of crassicaulisine, C (24)H (39)O (7)N, has been elucidated as 3 on the basis of chemical and spectral data, while the structure of crassicaulidine, C (24)H (39)O (8)N, has been shown as 4 on the basis of chemical data and spectral comparison with crassicaulisine.