Lithium garnet oxides of the composition series Li7-xLa3Zr2-xTaxO12 (x = 0-2) were synthesized by the solid state reaction and characterized by the powder X-ray diffraction and the impedance spectroscopy. Single cubic phases were obtained between x = 0.2 and 2, while the end-member Li7La3Zr2O12 exhibited a tetragonal phase. The lattice parameters of the cubic series followed the Vegard's law. The maximum bulk (9.6 x 10(-4) S/cm) and total (6.9 x 10(-4) S/cm) conductivities were achieved at x = 0.3 and x = 0.2, respectively at room temperature. Electrochemical tests with a hybrid solid vertical bar liquid electrolyte configuration were performed to evaluate the electrochemical performance of the solid electrolytes.