Cerium-doped Gd3(Al,Ga)5O12 powders have been synthesized with ultrasonic-assisted chemical coprecipitation method (UACC), and the traditional chemical coprecipitation method (CC) was also employed for comparison. The structure and morphology of powders were investigated by XRD, BET, and TEM. The powders were used for preparing ceramics at different temperatures. The specific surface areas of UACC and CC powders calcined at 800°C were 66 and 29 m2/g, respectively. Ceramics derived from UACC and CC powders were sintered at 1600°C, and the densities are 6.67 and 6.48 g/cm3, respectively. UACC is an attractive method for synthesizing GAGG powder for preparing ceramic scintillators.