The structure and capacitive properties of carbon spheres synthesized by heat treatment after hydrothermal carbonization of glucose were investigated. X-ray diffraction, Raman spectroscopy, and C-13 NMR spectroscopy measurements revealed that the spheres formed by polymerization of 5-(hydroxymethyl)-2-furaldehyde derived from glucose contained a small amount of microcrystalline graphite. N-2 adsorption analysis showed that heat treatment was effective for carbonization and nanopore formation in the carbon spheres. The capacitive properties of the carbon spheres were improved by heat treatment because their specific surface area increased and internal resistance decreased. The capacitance of carbon spheres heat treated at 800 degrees C was 115 F/g, which was higher than that of commercial activated carbon (90 F/g). (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V.