We investigated the microstructures and electrical properties of ZrO2 films deposited by reactive dc magnetron sputtering on Si substrates for gate dielectrics applications. We observed that the refractive index value of the ZrO2 films increased with an increase in deposition powers and annealing temperatures. The ZrO2 films deposited at elevated temperatures are polycrystalline, and both the monoclinic and tetragonal phases exist in the films. Films with higher density and improved crystallinity are obtained at higher deposition temperatures. The interfacial oxide layer between ZrO2 films and Si substrates grew upon annealing in the O-2 gas ambient, which is due to the oxidation of Si substrates by the diffusion of oxidizing species from O-2 gas ambient. The accumulation capacitance value increased upon annealing in the N-2 gas ambient due to the densification of the films, while it decreased in O-2 gas ambient due to the growth of the interfacial oxide layer.