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The roasting of precipitated copper sulphide in a current of air has been investigated by thermogravimetric analysis in the temperature range 150–800° under isothermal conditions. Chemical analysis of the products was carried out at intervals in each case to determine the distribution of copper between the sulphide, sulphate and oxide forms, and X‐ray diffraction patterns were used to identify the state of the solid phases. During roasting, cupric sulphide is converted to the cuprous state, formation of sulphate increases with rise of roasting temperature to a maximum at 400° and then decreases, while the copper oxide content increases with rise of roasting temperature first as cuprous oxide at the lower temperatures and then as cupric oxide above 500°. A mechanism of the roasting process is proposed which accounts for the variations of the relative amounts of sulphide, sulphate and oxide formed, and the state of oxidation of the first and last compounds.