The MnGeTe₂ compound crystallizes in a cubic structure without any phase transition and has great potential for enhancing the thermoelectric merit of MnGeTe₂-based materials. In this work, Sb was used as an effective dopant to replace Ge sites in MnGeTe₂ compounds. By optimizing the carrier concentration, excellent power factors can be obtained in the tested temperature range. Meanwhile, the characterization results show that Sb doping introduces point defects and induces grain refinement, which enhances phonon scattering and improves thermoelectric transport performance by reducing lattice thermal conductivity. Eventually, the ZT value increases from ∼0.65 for pure phase MnGeTe₂ to ∼0.84 for MnGe_0.90Sb_0.1Te₂ at 717 K by synergistic regulation of the electrical and thermal conductivities. In addition, the hardness test results of the samples show that the doping of Sb endows the MnGeTe₂-based thermoelectric material with a higher Vickers hardness (>200 H_V) and shows favorable mechanical properties.