The eutectic composition between Y4Al2O9and Y2O3was determined using electron probe microanalysis (EPMA) on directionally solidified specimens with hypo‐ and hypereutectic compositions. The microstructures of the specimens as a function of composition differ considerably with small deviation from the eutectic composition (70.5 mol% Y2O3and 29.5 mol% Al2O3). Based on the current results and other published data, the pseudobinary system between Al2O3and Y2O3is revise