We prepared In_xPb_xCo₄Sb[Formula: see text] by high-pressure and high-temperature (HPHT) method. Samples were characterized by X-ray diffraction (XRD), electron microprobe analysis and thermoelectric properties measurements. The Seebeck coefficient, electrical resistivity and thermal conductivity of In_xPb_xCo₄Sb[Formula: see text] samples were all performed in the temperature range of 323–723[Formula: see text]K. With the increasing synthetic pressure, the Seebeck coefficient of In[Formula: see text]Pb[Formula: see text]Co₄Sb[Formula: see text] samples, which synthesized between 1.5 GPa–2.3 GPa, showed an obvious increase while the thermal conductivity exhibited a substantial reduction.