A composite structure with two separately doped phases was introduced into Ni-doped LaCoO3 ceramics to enhance its electrical conductivity while keeping low thermal conductivity. LaCo0.9Ni0.1O3−δ nanoparticles were dispersed in the sol solution of La0.9Sr0.1Co0.9Ni0.1O3−δ and separated from the solution by centrifugation, which were then calcined and consolidated using normal sintering in air. The electrical conductivity of the coated samples was obviously increased, although the Seebeck coefficient was slightly decreased by the above particle- coating method, resulting in a great improvement of power factor. The Seebeck coefficient and electrical conductivity are strongly dependent on the concentration of La0.9Sr0.1Co0.9Ni0.1O3−δ sol, which affects the coating content, but the thermal conductivity is less affected by its concentration especially at room temperature. The power factor was increased to 2.58 × 10−4 Wm−1 K−2 at room temperature, resulting in a twofold enhancement in a peak ZT value at 373 K for the coated sample as compared with that without coating.