Abstract: A new coumarin(Ⅰ)was isolated from the roots and rhizomes of Glycyrrhiza inflata Bat.Its structure was elucidated as 4-(4'-hydroxy-phenyl)-6-prenyl-7-hydroxy-coumarin on thebasis of ¹H-,¹³C NMR,¹H-¹H,¹³C-¹H COSY,COLOC and NOEDS spectra ,and was named asinflacoumarin A。It was shown to markedly scavenge O₂^- produced by riboflavin under light。