The (Pb, La) (Zr, Ti)O3 ceramics were hot-pressed, and a micro-indentation technique was applied to the ceramics before and after poling. Internal stress anisotropies induced by application of dc electric field was found. The fracture toughness increased for the parallel direction to a poling field and decreased for the perpendicular direction due to a compressive and a extensional stress, respectively. The stress anisotropy disappeared by thermal depolarization at above Curie point. The results were explained by a ferroelectric domain rearrangement.