The amount of H2S evolved during pyrolysis was analyzed by g.c.-m.s. for four types of raw coal samples, Taiheiyo, Datong, Wandoan and Mequinenza. These coals were treated with HNO3 or HF/HCl solution, in which inorganic sulfur was eliminated by the acid treatment. In the case of HNO3-treated samples, the evolution of H2S in the low temperature region, below 500 degrees C, was reduced by the chemical oxidation. At high temperatures, the amount of H2S evolution from acid-treated coal was markedly increased compared to the raw coals, especially Taiheiyo and Wandoan, through the elimination of minerals. From X-ray fluorescence analysis and X-ray powder diffraction of coal and char, it was confirmed that calcium in the raw coal has an important role for:he fixation of sulfur during pyrolysis.