Compositionally “mixed” (yttria-scandia) sesquioxide transparent ceramics doped with erbium ions, ∼7 at.% Er:(ScxY1-x)2O3 (where x = 0–0.445) were fabricated by vacuum sintering at 1750 °C for 5 h using 1.7 mol% ZrO2 as a sintering additive. For this, nanopowders of the same composition obtained by laser ablation and sedimentation were used. The as-prepared nanoparticles (monoclinic sp. gr. C2/m) had a mean size of 20 nm and they were transformed into the stable cubic phase by calcination at 870–1150 °C. The ceramics were of single-phase nature (C-type bixbyite structure, sp. gr. Ia-3). For the (Er0.074Sc0.114Y0.812)2O3 ceramic, the lattice constant was a = 10.5067 Å, the mean grain size – 21.6 μm, the average content of pores – 4.2 ppm and the transmission at 1.1 μm - 81.9%. The X-ray diffraction and Raman studies of ceramics confirmed the existence of a solid-solution composition. With increasing the Sc3+ content in the ceramics, their lattice shrinked, the mean grain size increased and the thermal conductivity decreased from 6.14 to 3.66 Wm−1K−1 at room temperature. The “mixed” ceramics exhibited intense inhomogeneously broadened emission around 2.8 μm making them promising for mid-infrared lasers.