Process of oxidative desulphurisation of sulphur-rich containing Ukrainian coal was carried out in the temperature range of 623-723 K by air/steam mixture in the fluidised bed reactor. Mossbauer spectroscopy was applied to study the reaction products in form of iron compounds after every step of thermal treatment. The pyritic sulphur that constitutes most of total sulphur oxidises selectively at these conditions. At lower temperature (623 K) the ferrous sulphates and pyrite oxidised mainly to the ferric sulphate. At 673 K and higher temperatures alpha-Fe2O3 and SO2 were basic products of FeS2 oxidation. The transformation of FeS2 into pyrrhotite as the first stage of desulphurisation was observed at 698 K independently of the partial pressure of oxygen. The iron monosulphide (FeS) was not found at any stage of desulphurisation suggesting the pyrrhotite Fe1-xS oxidation before the sequential FeS2 --> Fe1-xS --> FeS transformation. (C) 2004 Elsevier Ltd. All rights reserved.