The structures of two new diterpenoid alkaloids, secojesaconi-tine Op and subdesculine (5), from Aconitum japonicum Thunb. were determined on the basis of spectral and chemical evidence. The structure of an unusual epoxide (1) was confirmed by X-ray analysis and was the first example of an epoxy ring between C3 and C17. Treatment of the epoxide (1) with acetic acid and acetylation were found to afford the normal C19-aconitine type alkaloid. © 1988, The Pharmaceutical Society of Japan. All rights reserved.