Bulk ceria-zirconia solid solutions (Ce 1−xZr xO 2−δ, CZO) are highly suited for application as oxygen storage materials in automotive three-way catalytic converters (TWC) due to the high levels of achievable oxygen non-stoichiometry δ. In thin film CZO, the oxygen storage properties are expected to be further enhanced. The present study addresses this aspect. CZO thin films with 0 ≤ x ≤ 1 were investigated. A unique nano-thermogravimetric method for thin films that is based on the resonant nanobalance approach for high-temperature characterization of oxygen non-stoichiometry in CZO was implemented. The high-temperature electrical conductivity and the non-stoichiometry δ of CZO were measured under oxygen partial pressures pO 2 in the range of 10 −24–0.2 bar. Markedly enhanced reducibility and electronic conductivity of CeO 2-ZrO 2 as compared to CeO 2−δ and ZrO 2 were observed. A comparison of temperature- and pO 2-dependences of the non-stoichiometry of thin films with literature data for bulk Ce 1−xZr xO 2−δ shows enhanced reducibility in the former. The maximum conductivity was found for Ce 0.8Zr 0.2O 2−δ, whereas Ce 0.5Zr 0.5O 2-δ showed the highest non-stoichiometry, yielding δ = 0.16 at 900 °C and pO 2 of 10 −14 bar. The defect interactions in Ce 1−xZr xO 2−δ are analyzed in the framework of defect models for ceria and zirconia.