In the work 12CaO-88ZrO ₂ (12CSZ, mol%) ceramics was manufactured both from nanopowder, obtained via cryochemical technique, and composite precursor 12CSZ + 0.25 wt% rGO (reduced graphene oxide). Via SEM, XRD and Raman spectroscopy the detailed investigation of the effect of the precursor type and intermediate processing on the microstructure and electrical conductivity of ceramics was carried out. It was shown that rGO is completely removed during the annealing at 1550 °C for 3 h in air with no effect on the high ionic conductivity of ceramics. The use of nanosized powder and the additional processing step results in vacuum dense solid electrolytes characterized by well-formed cubic zirconia based solid solution, thin discontinuous grain boundaries and rather high ionic conductivity. The addition of rGO leads to slight microhardness (HV) decrease comparing to ceramics manufactured from the nanosized precursor. As a result, a new technique for zirconia based solid electrolytes having both high electrical conductivity at high temperatures and sufficient mechanical properties was suggested.