Y3AlxGa5-xO12:Ce ceramics with an Al/Ga ratio from 5/0 to 0/5 was synthesized for the first time by direct impact of a powerful electron beam with an energy of 1.4 MeV on a charge of stoichiometric composition. The study results of dependence of the spectral properties and the conversion efficiency the excitation energy into luminescence on the ceramic composition are presented. A difference was found between the dependences of the efficiency of transformation of the excitation energy into luminescence on the Al/Ga ratio upon excitation of cerium ions at 450 and 337 nm.