Amorphous lithium tantalate (LTaO)- and lithium niobate (LNbO)-coated LiCoO2 (LCO) thin film electrodes were fabricated by pulsed laser deposition (PLD). The LTaO- and LNbO-coated LCOs showed lower interfacial resistances and high-rate charge discharge properties as compared with a bare LCO. The contribution of the LTaO and LNbO coatings to the electrochemical properties was considered using lithium diffusion and surface analysis. Tracer lithium diffusion coefficients (D-L1*) of the LTaO and LNbO thin films were determined by secondary ion mass spectroscopy (SIMS) using Li-6 and Li-7 isotopes. Surface analysis of the LTaO- and LNbO-coated LCOs before and after electrochemical measurement was performed using X-ray photoemission spectroscopy (XPS). The LTaO and LNbO thin films indicated fast lithium-ion diffusion; moreover, no degradation of the surface of the LNbO-coated LCO was observed during the electrochemical measurements. Therefore, LNbO is considered an excellent coating material for decreasing interfacial resistance.