The microstructure of permafrost ground contains clues to permafrost formation and hence its preconditioning to future change. We applied X-ray computed microtomography (CT) to obtain a high-resolution (Δx = 50 µm) dataset of the composition of a permafrost core drilled in a Yedoma upland in northeastern Siberia. The CT analysis employing image processing allowed to directly map and quantify excess ice, gas inclusions, and two distinct sediment phases. Using laboratory measurements of coarsely-resolved core samples, we statistically estimated the composition of the sediment phases and indirectly quantified pore ice, organic, and mineral contents. We conclude that CT is a promising method for obtaining physical properties of permafrost cores which opens novel research potentials. Title: Delineating the composition of a permafrost core using X-ray computed tomography Journal: The Cryosphere, Copernicus Publication