The thermal microstructural stability of Al2O3-Er3Al5O12 eutectic rods has been studied as a function of the solidification rate. The rods were directionally solidified by the Laser-Heated Floating Zone method, also known as Laser-Heated Pedestal growth technique. Their microstructures consisted of an interpenetrated network of both eutectic phases, whose size were controlled by the growth rate. The eutectics rods were heat-treated in air atmosphere at temperatures ranging from 1350 degrees C to 1650 degrees C up to 100 h. The coarsening kinetics was investigated from the evolution of the microstructure with the temperature and the time. The eutectics grown at 25 mm/h presented high thermal microstructural stability, with their microstructure remaining substantially unchanged even for the highest annealing temperature and the longest time. Eutectics grown at 350 mm/h experienced coarsening after 25 h at 1550 degrees C and those grown at 750 mm/h after 25 h at 1500 degrees C. Heterogeneous coarsening was found for heat treatments at 1650 degrees C. (C) 2011 Elsevier B.V. All rights reserved.