Gadolinium oxyorthsilicate doped with cerium, Gd 2 SiO 5 :Ce (GSO:Ce), is a scintillator crystal discovered in 1983, which has excellent properties, high light yield, fast decay time, and good radiation hardness. The Gd 2 SiO 5 (GSO) and GSO:Ce (0.5 mole%) single crystals were grown by Czochralski method under argon atmosphere. After the growth, thermal treatment of the GSO crystals was carried out at 1780K for 3 hours under argon atmosphere. The maximum wavelength of the emission spectrum of the GSO:Ce scintillator was 430 nm. The energy resolution of the GSO:Ce scintillator was 9.1 % with PMT, when it was exposed to 137 Cs γ-ray. The luminescence decay time of the GSO:Ce scintillator has two exponential components with 68.7 ns and 754 ns time constant.