Kusnezosines A-C (1-3), three C-19-diterpenoid alkaloids with a new skeleton which featured an undescribed lactone type D-ring, were isolated from the roots of Aconitum kusnezoffii Reichb. var. gibbiferum. Kusnezosines A-C are the first naturally occurred C-19-diterpenoid alkaloids which possessing an unprecedented lactone D ring, this structure was formed by the cleavage of bond between C-15 and C-16 and a successive lactonization. Their structures were established on the basis of comprehensive spectroscopic data analysis. Besides, another 12 known ones were isolated from this plant, analgesic activity tests on the isolated alkaloids were also carried out.