The purification of the MeOH extract from the aerial parts of Erythronium japonicum using column chromatography furnished a new megastigmane glucoside, erthrojaponiside (1), together with six known megastigmane derivatives (2 - 7). The structure of the new compound (1) was determined through 1D and 2D NMR spectral data analysis and chemical means. The isolated compounds (1 - 7) were tested for cytotoxicity against four human tumor cells in vitro using a Sulforhodamin B (SRB) bioassay.