A highly stable, water-based BaTiO3 sol system was developed by a chelate acetate sol-gel process. The BaTiO3 thin films and powders were prepared by a spin coating and drying-firing method, respectively, from the aqueous BaTiO3 sol. Structural evolution of the BaTiO3 gel was investigated by X-ray diffraction, Fourier transform infrared spectroscopy, and thermal gravimetric analysis/differential thermal analysis. Scanning electron microscopy microstructure results showed that the BaTiO3 thin films consisted of nano polycrystallites with a grain size of 30-60 nm, possessing a cubic perovskite structure. With ultraviolet light (UV) irradiation, the BaTiO3 films could be crystallized to a cubic phase at 550 degreesC. The dielectric measurement indicated no phase transition at the Curie temperature (125 degreesC). It is believed that the small crystallites having a cubic perovskite structure are responsible for the low dielectric constant and the flat temperature coefficient of capacitance behavior is due to the lack of the phase transition from the tetragonal to cubic phase.