A saponin (1) with gypsogenin as aglycone was isolated from the roots of Pulsatilla cernua. The aglycone of compound 1 was considered as gypsogenin which was rarely found in this genus. Its structure was predicted by NMR-based "mosaic" method rapidly, and further confirmed on the basis of spectroscopic data, including 2D NMR spectra and chemical evidence. This work suggested that NMR-based mosaic method is suitable for most of saponins from common species of genus Pulsatilla.