Phase relations in the system Cu-V-S were studied by using a sealedcapsule technique, reflected-light microscopy, X-ray powder diffraction and electron microprobe analysis. In the temperature range between 300 and 900 °C, six vanadium sulfides exist in the V-S system. These are VS, V 7S 8, V 3S 4, V 5S 8, V 3S 5 and VS 4. In the Cu-V-S system, three Cu-V sulfides are stable. Both Cu 3VS 4 (sulvanite) and CuV 2S 4 are cubic with a = 5.391 ± 0.005 A ̊ and a = 9.789 ± 0.005 A ̊ respectively, and the third has a composition Cu 0.8V 1.1S 2. CuV 2S 4 forms equilibrium assemblages with all vanadium sulfides, which restricts their effects on the phase relations in the system to a small region.