The effects of shot peening (SP) on the strength of partially stabilized zirconia (PSZ) were studied. The compressive residual stress, apparent fracture toughness (K (C)), and bending strength values of specimens subjected to SP were investigated. Results of x-ray diffraction analyses showed that SP introduced large compressive residual stress in specimens. As a result, the K (C) and bending strength values of specimens having semi-elliptical pre-cracks on their surfaces increased significantly. Shot-peened specimens having surface pre-cracks with lengths less than 140 A mu m exhibited strength comparable to that of smooth specimens and fractured outside the pre-crack zone, indicating that the pre-cracks were rendered harmless by SP. Thus, the introduction of a compressive residual stress by SP is an effective technique for increasing the strength of PSZ.