The perovskite electrolyte Li0.33La0.557TiO3 (LLTO) exhibits high mechanical stability, high ionic conductivity, and low strain during cycling. The cycle stability has been significantly improved using LLTO as a coating material for cathode particles. However, the electronic conductivity of LLTO is very low, which affects electrochemical performances. In this study, variable-valence elements (Fe, Ni, Co, and Cr) are added to the perovskite to increase the electronic conductivity. The materials are fabricated using a high-temperature solid-state reaction method. The phase compositions are characterized by X-ray diffraction (XRD), while the microstructures are analyzed by scanning electron microscopy. The electronic conductivity of the doped sample is increased by three orders of magnitude, while the ionic conductivity is slightly reduced. The Cr-doped sample exhibits the highest electronic conductivity of 9.18 x 10(-7) S cm(-1). The search for mixed conducting perovskites paves the way for the development of efficient coatings for cathode particles.