Polish high-sulphur coal was twice subjected to reduction in the potassium-liquid ammonia system. The process was carried out on both raw and demineralised coal. Elemental and spectral analyses of the initial coal and the reduction products were performed. Different forms of sulphur found in the samples were studied by the classical chemical methods and by atmospheric pressure-temperature programmed reduction (AP-TPR). The effect of reduction on particular sulphur compounds is discussed. It was found that reduction in the potassium-liquid ammonia system led to cleavage of C-S bonds, appearance of thiol groups, and the partial removal of pyrite and sulphates from the coal whereas the content of elemental sulphur did not change significantly.