A number of alkaloids have recently been isolated from Pachysandra terminalis SIEB. et ZUCC. (Buxaceae) and most of their structures have been established. This communication deals with the structure elucidation of spiropachysine (Ia), a major alkaloid from the plant's leaves (C₃₁H₄₆ON₂, m.p. 290-292°C, [α] +35°). Spiropachysine exhibits an IR band at 1673 cm⁻¹ (lactam) and its NMR spectrum reveals N,N-dimethyl, amide N-methyl, a sec-methyl, two tert-methyls, and a phenyl group. Through chemical transformations (LiAlH₄ reduction to deoxo compound II, MnO₂ oxidation of II to Ib, Hofmann degradation of II dimethiodide to methine base III, Emde degradation of II dimethochloride to IVb), spectral analyses (mass, IR, NMR) indicating it is a 20-dimethylaminopregnane-type alkaloid with a five-membered spiro-lactam, and synthetic confirmation (synthesis of IVa from epipachysamine-A, identical to IVa derived from spiropachysine), the structure of spiropachysine is assigned to Ia. NMR examination suggests the phenyl group probably has a β-configuration, with further stereochemical investigation ongoing.