The effects of leaching subbituminous coal samples from Boragolai and Ledo collieries of Makum coal field, Assam, India, with aqueous sodium hydroxide solution on removal of ash and sulphur, were investigated. Mild alkali treatment for relatively short period leads to removal of ash from the coal samples. Increase of alkali concentration and treatment time has negative effect on ash reduction due to formation and accumulation of insoluble sodium alummosilicate. Boragolai coal is less demineralized than Ledo coal and is attributed to presence of higher amount of alkali-soluble silica and alumina. Alkali treatment leads to over 70% removal of the inorganic sulphur in the coal samples. Desulphurization increases with increase in alkali concentration and treatment time. (C) 2003 Elsevier B.V All rights reserved.