Hafnium oxide (HfO₂) thin films were deposited on a silicon substrate using atomic layer deposition (ALD), and microwave annealing (MWA) was performed for different time. X-ray diffraction (XRD), Raman spectroscopy (Raman), atomic force microscopy (AFM), ultraviolet-visible spectroscopy (UV-Vis), ellipsometer (SE) and impedance analyzer were used to characterize the film performances. The effects of different microwave annealing time on the structure, optical and electrical properties of the film were studied in detail. The results show that the as-deposited HfO₂ film was amorphous, when the microwave annealing time is increased from 5min to 20min, the crystallinity of the HfO₂ film increases and the surface roughness decreases; but the dielectric constant decreases. In addition, the refractive index of the HfO₂ film hardly changes with the increasing of the microwave annealing time.