The effects of annealing on structure and laser-induced damage threshold (LIDT) of Ta 2 O 5 /SiO 2 dielectric mirrors were investigated. Ta 2 O 5 /SiO 2 multilayer was prepared by ion beam sputtering (IBS), then annealed in air under the temperature from 100 to 400 o C. Microstructure of the samples was characterized by X-ray diffraction (XRD). Absorption of the multilayer was measured by surface thermal lensing (STL) technique. The laser-induced damage threshold was assessed using 1064nm free pulsed laser at a pulse length of 220μs.It was found that the center wavelength shifted to long wavelength gradually as the annealing temperature increased, and kept its non-crystalline structure even after annealing. The absorbance of the reflectors decreased after annealing. A remarkable increase of the laser-induced damage threshold was found when the annealing temperature was above 250 o C.