The atomic layer deposition of Ta2O5 thin films was studied using a novel imido–amido precursor tBuN = Ta(NEt2)3. This precursor is liquid at room temperature, possesses good volatility and is reactive toward both water and ozone as the oxygen sources. The deposition temperature was varied from 125 to 475 °C. Saturated film growth was confirmed at 325 °C for both water and ozone processes, and a region of constant growth rate was observed between 125 and 350 °C when using ozone as the oxygen source. All the films were amorphous in the as-deposited state and crystallized at around 700 °C into orthorhombic Ta2O5, regardless of the applied oxygen source. X-ray photoelectron spectroscopy demonstrated high purity of the films deposited at temperatures higher than 225 °C. Atomic force microscopy revealed that the films were smooth (rms <0.3 nm) and uniform. The films exhibited permittivity values of ~25 and low leakage current.