A triterpene saponin, glucoglycyrrhizin, was isolated from a glycyrrhizin-deficient strain 83-555 of Glycyrrhiza uralensis (Leguminosae), and the structure was determined by chemical and spectral data to be 3-O-[β-D-glucopyranosyl-(1→2)-β-D-glucuronopyranosyl]-glycyrrhetinic acid. Since this saponin has a 2'-O-β-D-glucopyranosyl moiety instead of the 2'-O-β-D-glucuronopyranosyl moiety of glycyrrhizin, the glucuronidation of 3-O-β-D-glucuronopyranosyl-glycyrrhetinic acid leading to glycyrrhizin is inhibited in this strain. All 4 offspring of the 83-555 strain produced glucoglycyrrhizin. Interestingly, 2 of the offspring produced both glycyrrhizin and glucoglycyrrhizin, and sequence analysis of the pkr gene suggested that these 2 offspring were hybrids of 83-555 strain and glycyrrhizin-producing strains.