The paper reports the use of La 2 O 3 and ZrO 2 co-doping as a composite sintering aid for the fabrication of Tm:Y 2 O 3 transparent ceramics. Two groups of experiments were conducted for investigating the influences of composite sintering aids on the microstructures and the optical properties of Tm:Y 2 O 3 transparent ceramics in contrast to single La 3+ and single Zr 4+ doped Tm:Y 2 O 3 . Samples with composite sintering aids could realize fine microstructures and good optical properties at relatively low sintering temperatures. Grain sizes around 10μm and transmittances close to theoretical value at wavelength of 2μm were achieved for the 9at.% La 3+ , 3at.% Zr 4+ co-doped samples sintered at 1500–1600°C. The influences of the composite sintering aids on the emission intensities and the phonon energies of Tm:Y 2 O 3 ceramics were also investigated.