The combined effect of sonic energy and sodium hydroxide on the desulphurisation of different high sulphur and high ash content coals has been investigated in the temperature range from ambient to 60 degrees C and at atmospheric pressure. The sonication of coal samples led to a maximum reduction of 59 wt.% in total sulphur in a low rank coal, while 13 to 22 wt.% of total sulphur was removed from other sub-bituminous coals by employing a 1 M NaOH solution at 30 degrees C. Leaching under these conditions, a reduction of 53 wt.% in ash was achieved in a low ash content (6.8 wt.%) coal compared with 5-25 wt.% for high ash content coals. The effects of alkali concentration, coal particle size, temperature and time on the demineralisation efficiency of coals were investigated.