Thickness effect is studied experimentally. At free surface of the specimen, shear lip fracture pattern appears, though dimple fracture pattern is observed inside of the specimen. The area of shear-lip fracture changes due to the change of the specimen thickness. In this study, experimental study is conducted by changing specimen thicknesses. Fracture surfaces are precisely observed using SEM, and dimple patterns on them are observed. At the free surface, very narrow no-void area is observed. It is also found that many voids are nucleated in shear-lip fracture area. FEM simulation is carried out using Gurson’s constitutive equation. It is found that shear-lip type fracture is simulated near free surface area by this method. The results show similar tendency with the experimental observation.