A combination use of the ruthenium ion catalyzed oxidation reaction and measurement of solid-state C-13 NMR spectra was applied to the evaluation of the amount of bridge bonds and side chains in two brown coals. The distribution of carboxylic acids obtained from the oxidation reaction is applicable for determining the distribution of bridge bonds and side chains, while NMR data give the information on the amount of methyl group bonded directly to the aromatic ring. These data were utilized together for evaluating the bridge bonds and side chains quantitatively toward a coal molecule, the molecular weight of which is assumed tentatively as 10,000. As the results, it could be concluded that there are not so many long chains or bridges even in the brown coals, for example, less than 0.2 of C-5 chains are in an assumed molecule, however, the numbers of long chains and bridges in the assumed molecule of brown coal were found to be clearly greater than those in bituminous coal. (C) 2004 Elsevier Ltd. All rights reserved.