Several coal samples having different structures were successfully prepared from an Australian brown coal through liquid phase oxidation with H2O2 and HNO3. Since more than 90% of the oxidized coals were dissolved in dimethylformamide at room temperature, we could estimate the average structural parameters of the oxidized coals by spectroscopic analyses. These samples were subjected to flash pyrolysis to examine the effect of coal structure on the pyrolysis yield. The tar yield increased for the oxidized coal having a large amount of aliphatic carbon, whereas it decreased for the oxidized coal having a large amount of hydrogen bonding. It was found that the tar yield correlated well with the fraction of aliphatic carbon and the amount of hydrogen bonding determined from FT-IR spectra. (C) 2000 Elsevier Science Ltd. All rights reserved.