A new alkaloid, anhydrolycaconitine (C36H46N2O9), was isolated from roots of Aconitum septentrionale K. Based on the results of H-1 and C-13 NMR and IR spectroscopy and mass spectrometry of the alkaloid and the product of its alkaline hydrolysis and on the data of X-ray diffraction analysis of the hydrolysis product, the structure of 1 alpha ,6 beta ,14 alpha ,16 beta -tetramethoxy-7-oxo-18-succinylanthranoyloxy-17-(7 -->8)abeo-aconane was assigned to anhydrolycaconitine.