<jats:title>Abstract</jats:title><jats:p>A new 19,21‐secohetisan diterpenoid alkaloid, tangutisine B (<jats:bold>1</jats:bold>), was isolated from the aerial parts of <jats:italic>Aconitum tanguticum</jats:italic> (<jats:sc>Maxim.</jats:sc>) <jats:sc>Stapf.</jats:sc>, together with pacidine, 14‐deacetylajadine. The structure of <jats:bold>1</jats:bold> was determined by an interpretation of 1D‐ and 2D‐NMR together with X‐ray crystallographic data. Bioactivities of the isolates were tested in the P‐388, Bel‐7402, Cox‐2, and caspase‐3 assays.