Many kinds of alkaloids have been isolated from Amaryllidaceae plants, and some have interesting biological activities. For example, galanthamine and its n-butyl carbamate derivative were found to be centrally active competitive cholinesterase inhibitors and are undergoing clinical evaluation for the treatment of Alzheimer's disease. In the previous papers, we reported the isolation of a novel alkaloid incartine, a supposed biosynthetic intermediate in the pathway from galanthine to narcissidine, together with galanthamine from flowers of Lycoris incarnata. We now report the isolation and structural elucidation of two new alkaloids, 3-O-acetylnarcissidine (4) and 3-O-acetylnarcissidine N-oxide (5), together with the known alkaloids narcissidine (3) and lycorine (6) from Leucojum autumnale L. Crude basic material extracted from fresh bulbs of L. autumnale by the modified method of Wildman and Bailey was subjected to preparative thin layer chromatography (PTLC) to give compounds 3-6. Compound 3 was identified as narcissidine by comparison of its physical and spectral data with those of an authentic sample. Compound 4 was assigned as 3-O-acetylnarcissidine based on its IR and 1H-NMR spectra, and confirmed by preparation of diacetylnarcissidine from both 3 and 4. Compound 5 was identified as 3-O-acetylnarcissidine N-oxide by its spectral data and reduction to 4. Lycorine (6) was confirmed by comparison with an authentic sample.