Two new prenylated coumarins, sinensins A and B, have been isolated from the roots of Spiranthes sinensis (Pers.) Ames. Their structures were elucidated as 5-gamma, gamma-dimethylallyl-8-[2-(2,6-dihydroxyphenyl)-3-dimethyl-but-2-enyol]-umbelliferon (1) and 4,6-di(gamma, gamma-dimethylallyl)-8-lavandulyl-umbelliferon (2) on the basis of spectroscopic analysis.