Bytizite (Cu₃SbSe₃) has attracted interest as a promising thermoelectric material because of its ultralow thermal conductivity; however, there are few experimental studies. This study investigated the optimal processing conditions for the synthesis of Cu₃SbSe₃ using mechanical alloying (MA) and hot pressing (HP). The MA powder exhibited an orthorhombic Cu₃SbSe₃ phase, which remained even after HP. However, secondary phases of permingeatite (Cu₃SbSe₄) and berzelianite (Cu_1.78Se) were also identified in the X-ray diffraction patterns. Thermal analysis revealed that the MA powder and HP compacts exhibited a large endothermic peak near 727 K, which corresponds to the melting point of Cu₃SbSe₃. Dense compacts with a relative density higher than 99% were obtained at HP temperatures above 573 K. Microstructural and elemental analyses confirmed the presence of the secondary phase Cu₃SbSe₄ in the matrix of Cu₃SbSe₃. However, the Cu_1.78Se phase could not be observed. All specimens exhibited an electrical conductivity of (0.66- 1.06) × 10³ Sm^-1, a Seebeck coefficient of 324-376 μVK^-1, and a power factor of 0.09-0.11 mWm^-1K^-2 at 623 K. The thermal conductivity was lower than 0.7 Wm^-1K^-1 in the measured temperature range, mainly due to the phonon scattering caused by the lone-pair electrons of Sb. A dip in thermal conductivity was observed at 423 K, which was possibly caused by the order-disorder transition of bytizite. The dimensionless figure of merit ZT increased with increasing temperature, and the maximum ZT was 0.16 at 623 K. (Received 6 January, 2023; Accepted 16 Fabruary, 2023)