The ion substitution characteristics of Y3+-doped (Tb0.8Y0.2)3Al5O12 transparent ceramics synthesized by a solid-state reaction and vacuum sintering are investigated. The sample sintered at 1 680 oC exhibits the best optical properties, yielding a transmittance >75% from 900 to 1 600 nm. The Verdet constant of this sample at 632.8 nm is –108.79 rad.T-1.m-1. X-ray diffraction (XRD) results show that all of the samples have a pure garnet crystal structure without secondary phases. The microstructure of the samples reveals homogeneous grain sizes that averages <10 \mu m.