– Two new diterpenoid alkaloids and eight known ones were isolated from the root of Aconitum leucostomum. Their structures were elucidated on the basis of extensive spectroscopic analyses such as HR-ESI-MS, 1D NMR and 2D NMR spectra. Compounds 1, 2, 5, 6 and 8 were tested for their antifeedant activity against Spodoptera exigua Hübner, and compound 2 showed antifeedant activity with an effective concentration for 50% feeding reduction (EC50) at 1.54 mg/cm2. © 2021 The Japan Institute of Heterocyclic Chemistry