The first natural enolic glycoside, asterolloside (1), was isolated from the starfish Asterias rollestoni Bell together with two known tetrasaccharides. The structure of asterolloside was primarily elucidated by analysis of 1D and 2D NMR spectroscopic data. The absolute configuration was unambiguously determined by single-crystal Cu-Kα X-ray diffraction analysis. Asterolloside showed moderate α-glucosidase inhibitory activity with an inhibitory rate of 37.9% at a concentration of 0.12 mg/mL