All Solid State Lithium Ion Batteries (ASS-LIB) have been attracting great attention due to their high temperature stability, energy density and safety. Cubic Li7La3Zr2O12 (LLZO) ceramic electrolyte is one of the most studied solid electrolyte because of its exceptionally high chemical stability against Li metal, air and moisture, thermal stability and very competitive ionic conductivity. In order to stabilize cubic LLZO, relatively high temperatures are required. On the other hand, it's possible to decrease sintering temperature and time with a stabilizer addition. In this study, 20-30 mol % Al containing LLZO electrolytes were prepared by solid state reaction method at varying sintering temperatures (1100 degrees C and 1150 degrees C) for varying sintering times (12 h and 24 h) and the characterization of resultant materials were carried out. XRD results showed that, small amount of other compounds such as LaAlO3 were present in the sample produced at 1100 degrees C-12 h along with the main phase of cubic LLZO structure. According to SEM images, the sintering temperature was found to be more effective than sintering time on the densification behaviour. Existing porosities were reduced when both sintering temperature and time were increased. Different amount of Al addition did not have an effect on the densification behaviour. Both intergranular and transgranular types of fractures were observed by SEM. Finally it was found that 30 mol % Al containing samples sintered at 1150 degrees C for 12 h showed mixed conductor behaviour, whereas for 24 h and 36 h pellets showed ionic conductor behaviour. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.