The compressive deformation mechanism of several fine-grained ceramics with additives was investigated using transmission electron microscopy and X-ray spectroscopy. In Y2O3-doped ZrO2, the superplastic deformation is due to the grain boundary sliding although no amorphous phase was observed at grain boundaries. Pure Al2O3 was hardly deformed, however, large strain was obtained in ZrO2-doped Al2O3 ceramics, in which very thin amorphous layers containing Zr atoms existed between Al2O3 grains. Deformation of this material was found to be caused via both grain boundary sliding and dynamic grain growth. In MgO-doped Al2O3, the deformation mechanism was analogous to that of ZrO2-doped Al2O3 except no amorphous phase existed at the boundaries.