Abstract: Sulphosalts in the system CuSbS₂-CuBiS₂ (chalcostibite-emplectite) form a complete solid solution series. Seven compositions with the general formula Cu(Sb_xBi_l−x)S₂ have been synthesized using dry methods at 310°C. All members of the series are orthorhombic (space group Pnma) and show smoothly increasing a and b cell parameters with substitution of Bi for Sb; the c cell parameter increases up to 50% CuBiS₂ substitution and then becomes constant. DSC experiments on CuBiS₂ show an endothermic heat effect (2.45 kJ/mol.) at 472°C due to the breakdown reaction to Cu₃BiS₃ (wittichenite) plus Bi₂S₃ (bismuthinite). With the addition of 10% CuSbS₂ to CuBiS₂, the decomposition temperature increases and the endothermic peak is broadened but the energy remains essentially the same (2.53 kJ/mol.). No evidence of this decomposition was observed when the amount of the CuSbS₂ component was >30%. The local structure and co-ordination of Cu in the samples were studied by EXAFS analysis of the Cu-K edge but no significant variation occurs in the local Cu environment. The Debye-Waller factor for the first shell of S atoms surrounding Cu in end member CuSbS² tends to be slightly smaller than for the intermediate solid solutions, suggesting that the tetrahedral Cu environments in the intermediate composition samples is somewhat more disordered than in the end-member. The low expansion characteristics along c appear to be controlled by the linkages between the (CuS₃ + BiS₂) sheets perpendicular to c being relatively inflexible.