The evolution of char structure during heat treatment was investigated using coal petrography and micro Raman spectroscopy (MRS). The heat treatment was in the temperature range of 300-1000 degrees C using inertinite-rich South African coals. Char morphology analyses, determined petrographically showed a significant increase in the amount of dense/solid chars as compared to porous chars as temperature increases. MRS results were given in terms of the I-D/I-G intensity ratios, band positions and bandwidths as a function of temperature. It was found that sp(2)-sp(3) bonding (reactive sites/crystallites) was created in dense chars (originating from inertinite particles) at the initial heat treatment temperature, and these sp(2)-sp(3) bondings were consumed later at high temperature. Earlier consumption of sp(2)-sp(3) bonding was observed in porous chars, since they were vitrinitic in origin and contained more reactive sites. The D1 and G bandwidths showed a significant change with heat treatment, which were further correlated with the amount of dense and porous char determined petrographically. Therefore, the use of MRS and petrography on chars enhances the understanding of char evolution on a structural level and may lead to enhanced understanding of coal combustion. (C) 2010 Elsevier B.V. All rights reserved.