Syntheses of estriol glucosiduronic acids were carried out employing Koenigs-Knorr reaction. Of these three 16- and 17-glucuronides were prepared from estrone 3-benzyl ether, and 3-isomer from estriol 16, 17-diacetate as shown in Chart 1. All the glucuronides thus obtained underwent hydrolysis with beef liver β-glucuronidase to furnish estriol and glucuronic acid.