Abstract: A perovskite-type composite oxide Ba_1.0Co_0.7Fe_0.2Nb_0.1O_3-δ(BCFN) was successfully synthesized by solid state reaction with BaCO₃, Co₃O₄, Fe₂O₃ and Nb₂O₅ powders as raw materials. The synthetical process and morphology of BCFN fine particles were studied by non-isothermal thermogravimetry and differential scanning calorimetry (DSC), X-ray diffraction analysis, and scanning electron microscope. The results show that during the synthesis process, BaCO₃、BaFeO_2.9 and BasNb₄O₁₅ phases firstly appeared, and after 10 h sintering at 1473 K, a cubic perovskite-type oxide Ba_1.0Co_0.7Fe_0.2Nb_0.1O_3-δ was synthesized. The overall reaction process is considered involving two stages. The first stage is addition reaction between BaCO₃ and CO₃O₄, Fe₂O₃, Nb₂O₅ particles and the second is solid solution reaction between BaCoO₃ and BaFeO_2.9, Ba₅Nb₄O₁₅ phases formed in the first stage. Oxygen escaping was observed during the second stage.