Continuing an investigation of the alkaloids of Aconitum orientale growing on Turkish territory, with the aid of various methods of electron-impact (EI) mass spectrometry and secondary-ion mass spectrometry (LSIMS), a new base oreaconine (1), C37H50N2O10 with M+ 682, was detected in the plant roots. Isolated via column chromatography, oreaconine formed a white amorphous powder readily soluble in usual organic solvents. Its perchlorate had a melting point of 157--159°C (from MeOH, foaming). The IR spectrum of the perchlorate showed absorption bands for OH group (3500 cm⁻¹), ester group (1720, 1260 cm⁻¹), benzene ring (1605, 1585, 770 cm⁻¹), and ether C--O bond (1100 cm⁻¹). The PMR spectra of oreaconine and its perchlorate revealed signals for N-ethyl group (0.98 ppm, 3H, t, J = 7.5 Hz), five methoxy groups, succinimidylanthranilic acid (SAA) residue (four aromatic protons between 7.25 and 8.09 ppm), and characteristic protons (H-14β geminal to a methoxy group at 3.45 ppm as a doublet of doublets, H-6α geminal to a methoxy group at 3.62 ppm as a broadened singlet). The EI mass spectrum of oreaconine had ion peaks at m/z 682 (M⁺, 2.0), 681 (1.0), 667 (3.9), 651 (C36H47N2O9, 100), 650 (47), 635 (31), 619 (20), 589 (13), 202 (C11H8NO3, 50), 174 (17), 146 (24). Comparison with mass spectra of septentrionine, deacetylambiguine, peregrine and reference information indicated oreaconine belongs to C19-diterpene alkaloids of the lycoctonine type, with one methoxy group at C-1, succinimidylanthranilic acid (SAA) residue at C-18, hydroxyl at C-7, and methoxy at C-8. Considering the co-presence of related alkaloids (lycoctonine, anthranoyllycoctonine, methyllycaconitine, lycaconitine) in A. orientale and biogenetic considerations, the most probable structure (1) was proposed for oreaconine.