From the roots of Aconitum crassicaule, four diterpenoid alkaloids were isolated. Two of these were identified as chasmanine (5) and yunaconitine (4). The other two, crassicauline A and crassicauline B, are new alkaloids. The structure of crassicauline A, C (35)H (49)O (10)N, has been elucidated as structure (1) on the basis of chemical and spectral data, while the structure of crassicauline B, C (27)H (31)O (4)N, is still to be determined.