With glycosyl ortho-alkynylbenzoates as donors, the highly efficient glycosylation of flavonoid 5-OH which are notorious for their low reactivity due to their involvement in the formation of strong intramolecular H-bonds was achieved under the catalysis of a Au(I) complex. Thus, a series of flavonoid 5-O-glycosides, including a kaempferol 5-O-disaccharide, were synthesized with good to excellent yields.