A wide angle of incidence (AOI) mirror at 266 nm was fabricated through electron beam evaporation for fourth harmonic laser systems. The optical and microscopic morphology of the mirror was characterized by a spectrophotometer, scanning electron microscope, X-ray diffractometer, and atomic force microscope. The reflectivity of the films reaches 93.2% at 266 nm in the range of 0- to 45-deg AOI. The mirror was annealed at temperatures of 200°C, 300°C, and 400°C, respectively. The characterization results indicate that the annealing of mirror at 400°C led to the crystallization of HfO2 in a monoclinic crystalline phase. The highly reflective band of the annealed films at 400°C is obviously shifted to the shorter wavelength by 8 nm at 0- to 45-deg AOI. The annealing temperature has no significant effect on the surface morphology and roughness of the film.