Toxic substances in Narthecium asiaticum Maxim. were isolated and purified, monitoring the oral toxicity in guinea pigs. The crude extract prepared from the methanolic extract of the plant contained 2 major saponins (C₈ and C₉), and 7 corresponding saponins (C_1-7) on TLC. The crude extract was fractionated by a conventional method for saponin preparation. The 1-butanol fraction was rich in C₈ and C₉, and showed oral toxicity. C₈ and C₉ were isolated by fractional precipitation and silica gel column chromatography. On the basis of C-13 and H-1 nuclear magnetic resonance (NMR) spectral data, and acid and enzymatic hydrolysis of C₉, C₉ was comfirmed to be a mixture of two furostanol saponins (C_9a, C_9b); a branched trisaccharide composed of galactose, glucose, and arabinose, was linked at 3β-C, and glucose at 26-C of sarsasapogenin and smilagenin. C₈ was considered to be a furostanol saponin containing xylose instead of arabinose in the structure of C₉. Oral administration of C₈ and C₉ caused diarrhea, proteinuria, hematuria and death in guinea pigs.