The thermal behaviors of the leaching of mechanically activated sphalerite were investigated for the first time by calorimetry. The specific granulometric surface area and the structural disorder sphalerite were also analyzed by X-ray diffraction laser particle size analyzer and X-ray powder diffraction (XRD) analysis, respectively. A new method to measure the mechanically activated storage energy of minerals was proposed by designing a thermochemical cycle that made mechanically activated and non-activated mineral reaching the same final state while leaching in FeCl3 solution. The results indicate that the mechanically activated storage energy of sphalerite rises with the increased grinding time and is closely related to the lattice distortions and crystallite sizes. The calorimetric results of the products from sieved in water or ethanol medium and the products from 2 h treatment of mechanically activated sphalerite under pure argon (99.99 vol.%) at different temperatures indicate that the mechanically activated storage energy of sphalerite is caused mainly by changes of the crystal structure, and the reactivity of mechanically activated sphalerite is difficult to lose. (C) 2003 Published by Elsevier B.V.