Ternary copper-containing sulfides Cu 12 Sb 4 S 13 and Cu 4 Sn 7 S 16 have attracted considerable interest since few years due to their high-efficiency conversion as absorbers for solar energy and promising thermoelectric materials. We report therein on the decomposition study of Cu 12 Sb 4 S 13 and Cu 4 Sn 7 S 16 phases using high temperature in situ neutron powder diffraction. Our results obtained at a heating rate of 2.5 K/min indicate that: (i) Cu 12 Sb 4 S 13 decomposes above ≈ 792 K into Cu 3 SbS 3 , and (ii) Cu 4 Sn 7 S 16 decomposes above ≈ 891 K into Sn 2 S 3 and a copper-rich sulfide phase of sphalerite ZnStype structure with an assumed Cu 3 SnS 4 stoichiometry. Both phase decompositions are associated to a sulfur volatilization. While the results on Cu 12 Sb 4 S 13 are in fair agreement with recent published data, the decomposition behavior of Cu 4 Sn 7 S 16 differs from other studies in terms of decomposition temperature, thermal stability and products of reaction. Finally, the crystal structure refinements from neutron powder diffraction data are reported and discussed for the Cu 4 Sn 7 S 16 and tetrahedrite Cu 12 Sb 4 S 13 phases at 300 K, and for the high temperature form of skinnerite Cu 3 SbS 3 at 843 K.