The fracture toughness in the lead-free relaxor ferroelectric (1Àx)(Na 1/2 Bi 1/2 ) TiO 3 -xBaTiO 3 was investigated utilizing the surface crack in flexure method. To allow a comprehensive assessment, unpoled, and poled samples from the rhombohedral, the tetragonal, and the morphotropic phase regime were considered. It was found that the fracture toughness is up to 23% higher for the poled state. In order to cover the transition from ferroelectric to relaxor phase, the temperature dependence of 0.97(Na 1/2 Bi 1/2 )TiO 3 -0.03BaTiO 3 was studied as well. Fracture toughness values of up to 2 MPam 1/2 were determined, which are considerably above data for lead zirconate titanate materials. The results are rationalized using a simple transformation toughening-type model in conjunction with investigations into the ferroelastic behavior. The presented model can be applied without fitting parameters but utilizes measurements of the coercive stress and remanent strain as well as the elastic modulus. K E Y W O R D Sferroelastic materials, fracture mechanics/toughness, lead-free ceramics, mechanical properties, relaxors