Fixation of sulphur by addition of varying quantities (1, 1.5 and 2 wt. %) of calcium carbonate during ashing at 800-degrees-C of low and high sulphur coals as also the medium sulphur lignites has been studied. The results show that the fixation of sulphur increases with increase in the percentage of added calcium carbonate, being maximum for 2% addition. The fixation in case of low sulphur medium coking coals is maximum (52-72%). The low range of 3-17% is observed for high sulphur Assam and Meghalaya coals. The fixation of sulphur has been explained on the basis that the principal sulphide mineral (FeS2) in the coal, undergoes decomposition, with the evolution of SO2, which, in turn, is captured by the additive (CaCO3) in the form of CaSO4. The variance in the degree of fixation of sulphur in case of low and high sulphur coals is explicable on the basis of more or less availability of the porous surface of the additive.