The effect of oxygen partial pressure on the microstructure, wettability, optical and electrical properties of sputtering-derived HfO₂ thin films has been systematically investigated by using x-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), atomic force microscope (AFM), UV–visible spectroscopy (UV–Vis), spectroscopy ellipsometry (SE), and electrical measurements. XRD results have shown that the HfO₂ thin films are all polycrystalline with monoclinic phase. Based on analysis from FTIR, a strong absorption peak centered at 1105 cm⁻¹ has been detected, indicating the formation of the interfacial layer. Reduction in particle size and decrease in root mean square (RMS) roughness of the HfO₂ thin films have been detected by SEM and AFM measurements with the increase in oxygen partial pressure. Meanwhile, the contact angle decreases and the wettability increases with increasing the oxygen partial pressure. Combined with UV–vis and SE, the optical function of HfO₂ thin films as functions of oxygen partial pressure has been determined. By means of electrical measurements, evolution of electrical performance of MOS capacitor based on HfO₂ gate dielectrics related with oxygen partial pressure has been investigated systematically.