Optical absorption of nanostructured Al2O3 was investigated. Results are as follows: (1) when the annealing temperature, Ta < 800 °C, two broad absorption bands are observed in the reflection spectrum; (2) when Ta > 1100 °C, six absorption bands appear in the reflection spectrum. The appearance of the pronounced absorption bands with peak energies of 6.0 ev, ~ 55 ev, 4.8 ev, 3.75 ev and 3.05 ev, respectively, demonstrates that a large number of color centers exist in nanostructured Al2O3, including the F+ center, the v-type center (V2−, V− and VoH- centers) and the Cr3+ impurity center and others.