Bi-Sb alloy is a promising thermoelectric material that has a good thermoelectric performance at temperature below the freezing point. This material is useful for Peltier refrigeration and/or thermoelectric power generation recovering cold potential from LNG. We attempted to synthesize nanoparticles of the Bi-Sb alloy through a modified polyol process. Two kinds of precursors, Bi(NO₃)₃·5H₂O and Sb(CH₃COO)₃ (total amount 3 mmol) were dissolved in tetraethyleneglycole (TEG, 60 ml). A reducing agent NaBH₄ (12 mmol) dissolved in TEG (10 ml) was added into the solution, then the Bi-Sb alloy was synthesized by heating to 373∼453 K. The synthesized particles in the solution were settled by centrifugation, washed with deionized water and ethanol, and dried under a vacuum. The reaction products were characterized by X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectrometry (ICP-AES) and transmission electron microscopy (TEM). Bi-Sb alloy phase was identified. Formation of the Bi-Sb alloy particles with nano size was confirmed. The particle size was increased with rising reaction temperature and alloy composition was controlled with molar proportion of the precursors.