Hydrodynamic properties, such as intrinsic viscosity and diffusivity, were measured to investigate the solution state characteristics of coal-derived materials in three organic solvents: toluene, pyridine, and N-methyl-2-pyrolidinone. A coal-derived asphaltene was prepared using coal liquefaction residue and was used as the solute. The translational diffusion coefficient of the coal-derived asphaltene was determined using the Taylor dispersion technique. The sphere equivalent hydrodynamic radius of the coal asphaltene was estimated to be 0.6-0.8 nm, depending on the solvent. The combined intrinsic viscosity and diffusion coefficient data suggest that the shape of coal asphaltene can be modeled as a prolate ellipsoid. (C) 2002 Elsevier Science Ltd. All rights reserved.