Ca₃Co₄O₉ ceramic has attracted considerable attention for its practical applications in thermoelectric devices. The thermoelectric properties of Ca₃Co₄O₉–based ceramics can be improved by controlling its composition, microstructure, and carrier conduction. We fabricated Ca_3-xSm_xCo₄O_9+δ by spark plasma sintering process in combination with Ca_3-xSm_xCo₄O_9+δ powders prepared by sol–gel method. The electrical conductivity and the Seebeck coefficient were simultaneously measured over a temperature range of 500-800 °C. The thermal conductivity was obtained by measuring thermal diffusivity and specific heat capacity. XRD patterns showed that all the samples were single monoclinic phase, and no secondary phase was detected. The substituting ions of Sm³⁺ did not change the crystal structure. The degree of crystallographic anisotropy was evaluated in terms of the Lotgering factor. The electrical conductivity significantly increased with the incorporation of Sm³⁺. The Seebeck coefficient showed a positive value over the measured temperature range, indicating p-type conduction. In this work, the temperature dependent thermoelectric properties of Ca_3-xSm_xCo₄O_9+δ were systematically investigated.