A new 19,21-secohetisan diterpenoid alkaloid, tangutisine B (1), was isolated from the aerial parts of Aconitum tanguticum (MAXIM.) STAFF., together with pacidine, 14-deacetylajadine. The structure of 1 was determined by an interpretation of ID- 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. © 2005 Verlag Helvetica Chimica Acta AG.