In shearing process, tool wear is important to provide constant quality of product. The influence of flow stress of product material on tool wear is investigated. Piercing process experiment is carried out 50,000 strokes under the different conditions of sheared material and the clearance between punch and die. The punch edge radius and the amount of tool side wear are measured to evaluate the variation of tool wear. Additionally, the shape of sheared surface is measured to investigate the influence of tool wear on the product shape. Furthermore finite element analysis of shearing process is carried out under the same condition to confirm the influential factor on tool wear. In the experimental result, punch and die edge radius similarly increase with increasing of stroke number. Tool side wear causes increasing of clearance. However, these tendencies are different for sheared material. The shape of sheared surface is affected by tool edge wear than tool side wear. From analytical result, tool wear is predicted qualitatively by using friction energy, which is calculated from relative slip velocity between tool and material and surface pressure. These values are affected by material flow stress. Friction energy increases with increasing of flow stress and it causes increasing of tool wear.