The structure of two new diterpene alkaloids, 3-epi-ignavinol (1) and 2,3-dehydrodelcosine (3), isolated from Aconitum japonicum var. montanum Nakai collected at Mt. Arafune, were elucidated. No previous chemical or taxonomic studies have been reported on an Aconitum species native to Mt. Arafune (Gunma prefecture). Chemical investigation of the roots of this plant (Aconitum japonicum var. montanum Nakai, so-called Yamatorikabuto) resulted in the isolation of two new diterpene alkaloids, along with the eight known bases, talatizamine, delcosine, neoline, isotalatizidine, hypaconitine, 14-O-acetyldelcosine, takaosamine and kobusine. The structure of 3-epi-ignavinol (1) was determined by spectroscopic analysis (high resolution mass spectrum, IR, 1H-NMR, 13C-NMR) and confirmed by X-ray analysis. The structure of 2,3-dehydrodelcosine (3) was deduced by spectroscopic data and confirmed by direct correlation with 2,3-dehydrodelcosine obtained by the NaBH4 reduction of takaonine.