In this paper, optical properties of Eu3+:Y2SiO5 have been investigated. 7FJ(J equals 0,1,2,3,4)$ARLR5D0,1,2 transitions of Eu3+- doped in Y2SiO5 crystal were studied by transmission spectra, fluorescence spectra, photoluminescence excitation (or absorption) spectra and site selective fluorescence spectra. Nearly fifty Stark energy levels are recorded in our experiments. The results show that the Eu3+ ions occupy two inequivalent sites whose spectral lines of 5D0$ARLR7F0 transitions are about 0.2 nm from each other in Y2SiO5 crystal. By analyzing these spectra we also find that both sites are centers of low symmetry. The X-ray powder diffraction pattern of Eu3+:Y2SiO5 shows that the crystal is monoclinic, and lattices constants a, b, c and (beta) is obtained by a simulation with the measured diffraction angles. The lattice constants a, b, c is found slightly larger but very close to those of undoped Y2SiO5 crystal.