<jats:title>Abstract</jats:title><jats:p>Two new C<jats:sub>20</jats:sub>‐diterpenoid alkaloids, named aconicarchamines A and B (<jats:bold>1</jats:bold> and <jats:bold>2</jats:bold>, resp.), were isolated from <jats:italic>Aconitum carmichaelii.</jats:italic> By UV, IR, MS, and 1D‐ and 2D‐NMR analyses, their structures were elucidated as 14,17‐dihydro‐14,17‐dihydroxyajabicine and 15‐<jats:italic>O</jats:italic>‐acetyllassiocarpine. Compound <jats:bold>1</jats:bold> is the third C<jats:sub>20</jats:sub>‐diterpenoid alkaloid with the lycoctine skeleton bearing an exocyclic C‐atom at C(14).