The influence of domain orientation on the mechanical properties of lead zirconate titanate (PZT) piezoelectric ceramics has been investigated using un-poled and poled PZT ceramics. Good mechanical properties, e.g., high elastic modulus and compressive strength, were obtained for the poled PZT ceramics due to strain hardening caused by more severe domain switching during the loading process compared to the un-poled ceramics. Fracture mechanics of the ceramics were influenced by the direction of the tetragonal lattice structure since cracks propagate along the long axis of the tetragonal structure (c-axis). Using x-ray diffraction and electron back scatter diffraction analysis, the domain switching characteristics could be clarified.