Fundamental understanding of the effect of operating pressure on the coal reaction behaviour is essential to the development of advanced clean coal technologies. In this paper, a series of experiments were conducted to characterise chars obtained from a drop tube furnace (DTF) and a pressurised drop tube furnace (PDTF), from which the effect of pressure on coal reactions during devolatilisation and combustion of pulverised coals has been studied. In particular, the measured data indicated that pressure significantly influences the coal swelling behaviour during devolatilisation, hence the structure and morphology of the char generated. More Group I char particles are formed at higher pressures. The char structure has been found to play a significant role in burnout of residual char and ash formation, with a significant effect of pressure. In general, at higher pressures, coal particles burn quicker and form finer ash particles. These findings have significant implication for the operation of the practical high-pressure entrained flow gasifiers.