Cubic phase Li₇La₃Zr₂O₁₂ (LLZO) is a promising solid electrolyte for all solid-state lithium-ion battery, due to its reasonable ionic conductivity, stable against metallic Li, wide chemical window, and thermal and chemical stability. The main aim of this thesis is to investigate the influences of different synthesis methods on the structure and electrochemical performance of LLZO. In this work, LLZO is fabricated by solid-state method and sol-gel method, and consequently pellets and thin films were made for electrochemical measurements. Various characterization techniques including X-ray powder diffraction with Rietveld refinement, atomic force microscope, and X-ray reflectivity are used to examine the phase, structure and surface morphology of LLZO pellets and thin films. Electrochemical impedance spectroscopy is used to obtain the ionic conductivities and activation barrier of Li₇La₃Zr₂O₁₂. Using the solid-state synthesis method, 0.24 moles Al doped LLZO electrolyte sintered under multi-step heating at 1200oC with pure oxygen flow shows pure cubic phase, while such a pure cubic phase electrolyte is obtained at 1000oC by sol-gel method. Furthermore, the lithium (Li) ionic conductivity of the LLZO electrolyte pellet made from sol-gel powder is 2.88x10⁻⁷ S/cm at 80oC with activity energy Ea=0.45eV. Comparatively, LLZO thin film grown on MgO(001) substrate has Li ionic conductivity of 1.89x10⁻⁶ S/cm at 80oC with activity energy Ea=0.45eV. This work demonstrates the possibilities of fabrication LLZO electrolyte using different methods.