The absorption spectra of undoped and Eu3+-doped Y2SiO5 single crystals before and after gamma irradiation were studied. Additional absorption peaks at 260～270 nm and 320 nm were observed in irradiated Y2SiO5 crystal with no annealing or hydrogen-annealing, which were respectively caused by F centers and O- centers. Owing to the abserence of oxygen vacancy, there was no absorption peaks of color centers in air-annealed Y2SiO5 crystal. Additional absorption band of Eu2+ ions, which peaked at 300 nm and 390 nm, were produced in irradiated and H2-annealed Eu3+∶Y2SiO5 crystal, except absorption bands of F centers and O- centers. Additional absorption increased with irradiation dose increasing. Air-annealing could decrease the concentration of color centers, and the H2-annealing could increase it.