Despite zirconia based ceramics is technologically important and applied as a solid electrolyte, the studies for new compositions with enhanced performance are carried out continuously. Zirconia-graphene composites are regarded as promising oxygen transport membranes having a cross-flow of ionic and electronic charge carriers under oxygen partial pressure gradient and as an alternative to perovskite-based SOFC interconnects. In the work 92ZrO₂-8Y₂O₃ (mol.%, YSZ) ceramics and YSZ-rGO composite ceramics (where rGO is reduced graphene oxide) were obtained from composite precursors by the calcination at 1823 K in air and in vacuum, respectively. In order to determine the optimal amount of rGO addition to the ceramic precursor simple mathematical model was suggested for the first time which is scalable for any ceramics-graphene derivative and metal-graphene derivative systems. Using SEM, EDX, XRD, Raman spectroscopy and Impedance spectroscopy data the effect of rGO and the annealing ambiance on the structure, temperature dependencies of grain and grain boundary conductivities of YSZ ceramics rGO-YSZ and composites were revealed for the first time. The rGO additive acts as grain growth inhibitor, which is completely removed from ceramics during annealing in air resulting in ceramics with the refined microstructure and coinciding temperature dependencies of grain and grain boundary conductivities in all temperature range. Vacuum annealing results in YSZ-rGO composites with high ionic conductivity and high crystallinity.