Stoichiometric CaZrO 3 (CZ-50) and CaZrO 3 doped with excess CaO (CZ-51) powders, whose formula (CaO) 1−x (ZrO 2 ) x , where x=50 or 51mol.% CaO was successfully synthesised by the co-precipitation calcination method with a saturated solution of (NH 4 ) 2 C 2 O 4 in concentrated NH 3 solution as a precipitation agent. The thermal evolution of CaZrO 3 dried precursor during heating them up to 1200°C was monitored by thermal (DTA, TG) and X-ray diffraction analysis methods. The highest temperature (1200°C) for CaZrO 3 synthesis was found for stoichiometric CaZrO 3 , whereas introduction of excess CaO into CaZrO 3 led to a decrease in the synthesis temperature to 1000°C. The crystallite size d (hkl) of grounded CaZrO 3 powders ranged from ∼43 to ∼90nm, respectively. BET measurements indicated that in both the investigated powders, particles were agglomerated. Sintering CaZrO 3 -based samples at 1500°C/2h or hot-pressing process (1250°C/1h, 25MPa) was applied to obtain gas-tight CaZrO 3 -based ceramics. To examine the thermochemical stability of materials obtained at high temperatures, the CaZrO 3 -based samples were additionally heated at 1200°C for 120h or in the temperature range 1400–1600°C for 24h in air or purified argon. There were also performed and then discussed, some tests on thermal resistance of CaZrO 3 against molten metals—nickel and copper. Investigations into chemical reactivity of CaZrO 3 electrolyte with electrode materials involving LaCrO 3 or MCr 2 O 4 (M=Mg, Ca) in the temperature range 1000–1200°C were conducted using XRD with Rietveld analysis. Electrical conductivity measurements performed by both dc and ac impedance spectroscopy method in the temperature range 200–1000°C. The best oxygen ion conductivity was found for CaZrO 3 -doped excess CaO (CZ-51) samples sintered in air, starting from powders synthesized by co-precipitation or citrate method. The CZ-51 samples obtained via solid state reaction or hot-pressed exhibited lower values of electrical conductivity. Test results for this compound used as an electrolyte in solid oxide cells involving electrode materials MCr 2 O 4 (M=Mg, Ca) are also reported. In this way the Gibbs free energy of formation of MgCr 2 O 4 at 1000°C was determined. The nonstoichiometric CaZrO 3 seems to be a promising solid electrolyte for electrochemical oxygen probes in control of metal processing.