Tanaconitine (1), a novel Aconitum alkaloid with a C29 skeleton, together with six known diterpenoid alkaloids, was isolated from the roots of Aconitum tanguticum. The structure of 1 was elucidated to be 17 dehydroxyl-30 a(cis-10 -methyl-30 ,30 a,70 ,70 a-tetrahydro-1H-indol-60 (2H)-one)-naviculine A by spectroscopic analysis.