Eleven alkaloids were isolated from the roots of Aconiti kusnezoffii. The structures of three new C20-diterpenoid alkaloids, named napellines C to E (1 - 3), were elucidated based on spectroscopic methods including HRESIMS, IR, and NMR, together with comparison of their spectroscopic data with those of known analogues in the literature. The plausible biogenetic pathway for napelline-type diterpenoid alkaloids is also proposed. In addition, napellines C to E (1 - 3), along with known napelline B, were evaluated in vitro for their proliferative activities against A549, HL-60, MCF-7, Bel-7402, BGC-823, and RAW264.7 cells. Among the compounds tested, napellines B and C at 50 mu M (vs. 5 mu M, p < 0.01) exhibited the significant proliferating activities against RAW264.7 cells and their proliferative rates were -62.1 % and -59.6 %, respectively.