Oxide-ion conductors have been widely studied because of their potential applications as components of fuel cells, oxygen sensors, oxygen pumps and oxygen-permeable membrane catalysts [1]. Up to now, there is a considerable number of structural families that could be suitable for use as oxide electrolytes in consideration of the limitation of operating temperature and conductivity. An oxygen ionic conductor, reported by Lacorre et al. [2], namely lanthanum molybdate La2Mo2O9 [3], has attracted much attention due to its high ionic conductivity at medium temperature (0.06 S/cm at 800 °C) [4]. This compound undergoes a structural transition around 540 °C, resulting in a decrease in conductivity by almost two orders of magnitude at low temperatures. Substituting the La3+ cation with divalent ions such as Ca, Sr, Ba etc. can suppress this phase transition and maintain the high-temperature phase to lower temperature with only slightly decreased or even increased conductivity in some cases. Up to now, various synthesis methods have been developed to synthesize lanthanum molybdate substituted by different cations. Aqueous sol–gel synthesis method is one of the simplest preparation techniques that is successfully used for the obtaining of different materials with necessary physical and chemical properties. However, only limited investigations have been published on the thermoanalytical study of the as prepared gel precursors by the formation of the La2Mo2O9 substituted with divalent Ca2+. Moreover, the influence of used starting materials to the resulting surface morphology of produced ceramics also was not investigated in detail. We present the investigation of Ca2+ substituted La2Mo2O9 by thermoanalytical analysis of gel precursors and microscopy of surface of subsequently sintered ceramics. Furthermore, the samples, which characterized by a dense surface morphology, were additionally studied by two different electrical impedance spectroscopy techniques.