Samples of Li7La3Zr2−0.75x Al x O12 (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30) were synthesised using the citrate–nitrate method. The crystal structure of each sample was characterised using X-ray diffraction. Doping the samples with Al reduced the synthesis time. The cubic modification of Li7La3Zr2O12 was obtained by treatment at 1150 °C for 1 h. The conductivity of the ceramic samples was studied by complex impedance spectroscopy at 25–230 °C. The composition with x = 0.15 had the highest total conductivity, 3.4·10−4 S cm−1, at 25 °C.