A chemical investigation on the roots of Aconitum episcopale afforded three undescribed aconitine-type C-19-diterpenoid alkaloids, episcopalines A-C (1-3). The structures of the new compounds were elucidated by spectroscopic analysis (NMR, IR, UV, and MS). The isolated alkaloids were tested in vivo for their antinociceptive properties. As a result, episcopaline B (2) showed potent antinociceptive effect and its ID50 value (55.0 mu mol/kg) was 2-fold less than those of the positive control drugs aspirin and acetaminophen.