12-Epinapelline and its N-oxide have been isolated from the epigeal part of Aconitum baicalense Turcz. ex Rapaics (A. Czekanovskyi Steinb.). The structures of these compounds were determined using two-dimensional 1H and 13C NMR spectroscopy, infrared (IR) spectroscopy, and mass spectrometry. For the minor terpene bases, the chloroform-soluble fraction of total alkaloids was chromatographed on alumina to isolate base (I). Base (I) had a molecular mass of 375 a.m.u. and elementary composition C22H33O4N. Its IR spectrum showed an absorption band at 905-920 cm-1, indicating an N-oxide functional group. Analysis of 1H and 13C NMR spectra revealed three oxygen-containing functions, an exomethylene double bond, an N-ethyl group, and a C-methyl group (attached to a tertiary carbon), suggesting a napelline carbon skeleton. Detailed NMR studies at 500 MHz using double-resonance techniques (COSY, HETCOR) assigned base (I) the structure of 12-epinapelline N-oxide. Comparison with flavamine (II) showed differences in spectral characteristics for C-12, O13, C-16, and C-17 atoms, indicating a stereochemical difference at C-12: the H-13 signal at 2.80 ppm (doublet of doublets, J=8.7, 4.1 Hz) implied an axial orientation of the 12-hydroxy group (β-orientation). Additionally, 12-epinapelline (III) was isolated together with napelline. Its spectral characteristics—including a PMR signal for H-13 at 2.78 ppm (doublet of doublets, J=9.0, 4.0 Hz) and a 13C NMR spectrum analogous to that of 12-epinapelline N-oxide (I) but distinct from napelline—confirmed the β-orientation of the 12-hydroxy group, leading to the assignment of structure 12-epinapelline (III).