In　order　to　uncover　the　intrinsic　reasons　for　spontaneous　combustion　of　sulfide　minerals,　representative　samples　were　collected　from　typical　metal　mines　to　carry　out　the　mechanical　activation　experiment.　The　structures　and　heat　behaviors　of　activated　samples　were　characterized　by　scanning　electron　microscopy　(SEM),　X-ray　diffraction　(XRD)　analysis,　and　simultaneous　thermal　analysis　(STA).　It　is　found　that　the　sulfide　minerals　after　mechanical　activation　show　many　changes　with　increased　specific　surface　areas,　aggregation　phenomenon,　decreased　diffraction　peak　intensity,　broadened　diffraction　peak,　declined　initial　temperatures　of　heat　release　and　self-ignition　points.　A　new　theory　for　explaining　the　spontaneous　combustion　of　sulfide　minerals　is　put　forward:　the　chemical　reaction　activity　of　sulfide　minerals　is　heightened　by　all　kinds　of　mechanical　forces　during　the　mining,　and　the　spontaneous　combustion　takes　place　finally　under　proper　environment.　©　2013　The　Nonferrous　Metals　Society　of　China.