We have investigated the alkaloidal constituents of the roots of Aconitum ibukiense NAKAI collected at Mt. Ryosen (Shiga Pref.). In addition to the known twelve compounds i.e. mesaconitine, hypaconitine, aconitine, deoxyaconitine, 14-dehydrobrowniine, 14-dehydrodelcosine, delcosine, takaonine, neoline, 15-α-hydroxyneoline, senbusine A, and ignavine, four new bases, i.e. ibukinamine, ryosenamine, ryosenaminol, and 9-hydroxynominine, were isolated. The structures of ibukinamine, ryosenamine, and ryosenaminol were established to be 2.3-dehydro-6-O-demethyldelcosine, 1-deoxyhypognavine, and 1-deoxyhypognavinol, respectively, by the spectroscopic evidence and by the X-ray crystallographic analyses. The structure of 9-hydroxynominine was deduced by the spectroscopic evidence.