Abstract: Transformation zone in a single-edge notch bending specimen of ceria-stabilizedtetragonal zirconia polycrystal was studied by moire interferometry.The transformationzone with a characteristic elongated shape ahead of the notch was observed and the distri-bution of plastic strain within the transformation zone was obtained from the moire fringepatterns. This work provides a significant experimental foundation for establishing the the-oretical models of transformation toughening.