A comparative study of the thermal non-oxidative decomposition of tetrahedrite Cu12Sb4S13 ground in a planetary mill has shown that the mechanical activation does not change the mechanism of this decomposition but has positive influence on its rate. The formation of agglomerates from finely ground particles of tetrahedrite restricts the extent of this influence. Bornite Cu5FeS4 and digenite Cu1.765S were identified in the decomposition products obtained at 773, 893 and 1113 K. The values of activation energy found for the decomposition in the temperature region 765-972 K indicate that diffusion is the rate-determining process.