Chalcostibite (CuSbS₂) is composed of earth-abundant elements and has a proper band gap (E_g = 1.05 eV) as a thermoelectric (TE) material. Herein, we report the TE properties in the CuSbS₂ based composites with a mole ratio of (1-x)CuSbS₂-xCu_1.8S (x = 0, 0.1, 0.2, 0.3), which were prepared by mechanical alloying (MA) combined with spark plasma sintering (SPS). X-ray diffraction (XRD) and back-scattered electron image (BSE) results indicate that a single phase of CuSbS₂ is synthesized at x = 0 and the samples consist of CuSbS₂, Cu₃SbS₄, and Cu₁₂Sb₄S₁₃ at 0.1 ≤ x ≤ 0.3. The correlation between the phase structure, microstructure, and TE transport properties of the bulk samples is established. The electrical conductivity increases from 0.14 to 50.66 S·cm^-1 at 723 K and at 0 ≤ x ≤ 0.03, while the Seebeck coefficient holds an appropriate value of 190.51 μV·K^-1. The highest ZT value of 0.17 is obtained at 723 K and at x = 0.3 owing to the combination of a high PF 183 μW·m^-1·K^-2 and a low κ 0.8 W·m^-1·K^-1.