Abstract: A new selaginellin derivative named as selaginellin S (1) was isolated from the whole plants of Selaginella pulvinata (Hook. et Grev.) Maxim. (Selaginellaceae), together with a known one (selaginellin M, 2). Compounds 1 and 2 were separated and purified by silica gel and Sephadex LH-20 column chromatography. Their structures were determined on the basis of extensive spectroscopic analysis including IR, MS, 1D and 2D NMR experiments, as well as ECD calculations. Compound 1 is a key intermidiant in the biosynthesis pathway of selaginellins. Compound 2 is first reported in this plant.