An efficient and convenient procedure for the synthesis of estriol 16- and 17-monoglucuronides from estriol is described. This is achieved by the selective protection and deprotection of the hydroxy groups in estriol, Koenigs-Knorr reactions with methyl 1-bromo-1-deoxy-2,3,4-tri-O-acetyl-alpha-D-glucopyranuronate and subsequent hydrolysis. The products have been characterized by proton nuclear magnetic resonance (1H NMR), two-dimensional 1H homonuclear shift-correlated spectra (2D-COSY) and mass spectra. The selective Koenigs-Knorr reaction of the alcoholic hydroxyl group in the presence of a phenolic hydroxyl group is also reported.