The chemical structure of the oligosaccharide produced from sucrose by an enzyme extracted fromAureobasidium sp. ATCC 20524 was observed. The GC-MS analysis by methylation indicated that this oligosaccharide is composed of 2-linked, 1,2-linked fructose and 1-linked glucose. The [13C]-NMR spectrum indicated that the 1,2-linked glycosidic linkages of fructose of this oligosaccharide areβ, and the 1-linked glycosidic linkages of fructose are α. This investigation suggested that this oligosaccharide is isokestose.