In order to get a general regularity of erosion performance in alumina‐strengthened yttria ceramics, High‐quality yttrium‐aluminum oxide composite ceramics with different alumina/yttria molar ratios were fabricated, and the as‐prepared specimens were named Y2O3, YAG, YAGA, and Al2O3. The erosion behavior of the ceramics was examined and explained. The etching morphologies of the ceramics revealed that the multi‐phase composite ceramic (YAGA) was etched selectively, whereas the single‐phase ceramics were corroded homogeneously. The weight loss rate of the ceramics after etching was not proportional to the Al2O3 content, and it conformed to the percolation theory. As the alumina content in yttrium‐aluminum oxide composite ceramics was below the minimum value of percolation transition in two‐phase system the erosion resistance of the strengthened composite ceramics demonstrated excellent as well yttria ceramics.