A three phase ceramic composite of 8 mol% Y2O3 stabilized ZrO2 (YSZ), SiO2, and Al2O3 was evaluated for potential high temperature superplasticity. The amorphous SiO2 content was 5 wt.%, and increasing additions of Al2O3 were made. The effect of varying the Y2O3 stabilizer concentration in ZrO2 was also studied. Samples sintered at 1200 degrees C contained only YSZ, Al2O3, and amorphous SiO2, but ZrSiO4 formed in the samples above 1300 degrees C. Mullite (3Al(2)O(3) center dot 2SiO(2)) was not detected in any samples. Specimens of 1 wt.% Al2O3-YSZ/SiO2 had an anomalously high deformation rate of similar to 2 x 10(-4) s(-1) at 1200 degrees C when compared to YSZ/SiO2 without Al2O3 (similar to 4 x 10(-5) s(-1)). Higher amounts of Al2O3 additions decreased the strain rate. Extensive deformation of Al2O3 doped YSZ/SiO2 at 1200 degrees C induced the formation of ZrSiO4 due to enhanced reaction rates. This distributed, yet locally interconnected, zircon phase rapidly eroded the strain rate after -60% deformation.