Skutterudite CoSb3 compounds are of increasing interest as materials with good thermoelectric performance over the temperature range of 600 to 800 K, but the thermal conductivity of the materials is relatively high. Nanostructured materials have been shown to enhance phonon scattering and lower the thermal conductivity of the thermoelectric materials. Partial substitution of Ni or Fe on the Co site of CoSb3 is a hopeful route for improving thermoelectric performance of the CoSb3 compounds. In the present work, synthesis of Ni-doped and Fe-doped CoSb3 nanoparticles through the modified polyol process was attempted and the optimum synthesizing condition was investigated. Co(OOCH3)2·4H2O, Ni(OOCH3)2·4H2O, FeCl3·6H2O and SbCl3, were prepared as precursors. The precursors were reduced by NaBH4 in tetraethyleneglycol at 513 K in an argon atmosphere, for different reaction times (holding times). The reaction products were characterized by the X-ray diffraction, the energy dispersive X-ray spectroscopy, and transmission electron microscopy. The nanoparticles with about 20 to 30 nm in size mainly existed in the reaction products regardless of the chemical composition and the reaction time. The skutterudite phase was identified as a main phase in the sample synthesized for long reaction time, but the other phases of Sb and MSb2 (M=Co, Ni, Fe) were also detected. The lattice parameter of the synthesized skutterudite phase linearly increased with increasing the doping agent concentration, following Vegard’s law.