The high temperature mechanical properties of polycrystalline Y2SiO5 were studied in compression at temperatures in the range of 1200–1400 ◦C, both in constant strain rate andconstant stress experiments. To examine the effect of grain size on the plastic deformation,two routes were used for the synthesis and sintering of Y2SiO5: one of solid state reactionfollowed by conventional sintering in air, and one of sol–gel synthesis followed by sparkplasma sintering, resulting in starting grain sizes of 2.2 and 0.9m, respectively. Ceramicsobtained by these routes exhibited different high-temperature compression behavior: whilethe conventionally processed ceramic exhibited grain growth during mechanical testingand a stress exponent close to one, compatible with diffusional creep, the spark-plasmasintered ceramic showed no grain growth but significant cavitation, a stress exponent closeto two and partially superplastic behavior. These results have implications for the designand lifetime assessment of rare earth silicate-based environmental barrier coatings