The effect of HCl, HNO3 and H2SO4 at different concentrations on demineralization of high sulphur coal from Boragolai and Ledo colliery of Makum Coalfield, Assam, India was investigated at ambient and 95 degreesC. The acids, depending on type and concentration, can reduce the mineral matter in the range of 22.6-32.0% at ambient temperature and 24.8-40.1% at 95 degreesC from Boragolai coal. The acids at 10% concentration level can remove 7.6-22.6% and 13.6-38.6% sulphur from Boragolai coal at ambient and 95 degreesC, respectively. HNO3 leads to maximum and H2SO4 minimum desulphurization of the coal samples. The low desulphurization ability of H2SO4 is attributed to high viscosity of the acid at ambient temperature and sulphonation of the coal samples. The demineralization and desulphurization of Ledo coal with the acids are relatively low and is attributed to its higher hydrophobicity. (C) 2003 Elsevier B.V All rights reserved.