Nanocrystalline ceria-based thin films are of potential interest for use as gas-sensing layers and electrolytes in micro-Solid Oxide Fuel Cells (micro-SOFC) used for energy supply of next generation portables. In these devices the thin films have to be operated at intermediate to high temperatures (500 - 1000 °C) to be sufficiently high electrical conductive. However, only little is known on the nucleation and grain growth kinetics of pure ceria and its solid solutions when present as nanocrystalline thin film microstructures (average grain size < 100 nm). In this study amorphous, dense and crack-free CeO2 and Ce0.8Gd0.2O1.9-x thin films have been deposited by spray pyrolysis on sapphire. These films were crystallized to biphasic amorphous-nanocrystalline and fully nanocrystalline microstructures upon annealing with respect to time, temperature, heating rate and doping. Nucleation and grain growth kinetics were studied by differential scanning calorimetry, Xray diffraction analysis with in-situ heating chamber and scanning electron microscopy.