Transformation of pyrite in a demineralized subbituminous coal with various coal particle size distributions (PSD) during pyrolysis was investigated using a thermogravimetric analyzer coupled with mass spectrometer (TGA-MS). The residues from pyrolysis were examined by X-ray diffraction (XRD) and scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (SEM-EDS). It is found that the pyrite content is higher in coal with smaller particle size. The reduction of coal particle size is beneficial to the evolution of gaseous sulfur at 350-650 degrees C. The results from XRD and SEM-EDS analyses show that during pyrolysis small coal particles facilitate the formation of low-sulfur Fe-S phases and even elemental iron in char. The isolated pyrite crystals or the aggregates of pyrite are rich in coal with smaller particle size than in larger ones, and this is beneficial to the pyrite conversion and the formation of low-sulfur Fe-S phases in the finer char particles. (C) 2015 Elsevier Ltd. All rights reserved.