The pyrolysis of mesaconitine and hypaconitine which are present as strongly toxic components in the raw aconite roots was performed. C(15)-keto pyro type compounds 1, 4 were obtained by the pyrolysis of mesaconitine and hypaconitine, respectively and structures of those compounds were determined as 16-Epi-pyromesaconitine(1) and 16-Epi-pyrohypaconitine (4) having $C(16)-{alpha}-OCH_3$ on the basis of their spectral and chemical data.