By bioactivity-guided fractionation, three known steroidal glycosides, beta 2-solamargine (1), solamargine (2), and degalactotigonin (3), were isolated from Solanum nigrum. Compounds 1-3 induced morphological abnormality in Pyricularia oryzae mycelia with MMDC (minimum morphological deformation concentration) values of 63.0, 38.5, and 97.2 microM, respectively. This is the first report on the isolation of 1 from this species and on the cytotoxicity of 1-3 on six cultured human solid tumor cell lines HT-29 (colon), HCT-15 (colon), LNCaP (prostate), PC-3 (prostate), T47D (breast), and MDA-MB-231 (breast) in vitro. The cytotoxic assay indicated that 2 is the main antineoplastic agent in S. nigrum. The structures of 1-3 were elucidated on the basis of chemical evidence and spectral analysis, especially by 2D-NMR analysis.