Thermoelectric (TE) materials play a crucial role in waste heat recovery and energy harvesting, converting thermal gradients directly into electricity. Among the many materials studied, oxide-based thermoelectrics have attracted significant attention due to their thermal stability, environmental friendliness, and low cost. Yet they have historically functioned less well than traditional chalcogenide-based counterparts. The existing works have reported various RE doping as new tactics to improve TE performance by adjusting carrier concentration, enhancing Seebeck coefficient, and diminishing thermal conductivity. This chapter thoroughly examines the function of rare earth dopants in diverse oxide systems, including ZnO, CaMnO3, SrTiO3, and NaCo2O4. We emphasize the doping mechanisms, structural alterations, charge transport phenomena, and phonon scattering techniques introduced by rare earth (RE) elements.