The understanding of material characterization is necessary for metal forming process because the characteristic of material was directly related to the die designs. The die designers could adopt their knowledge to choose the appropriate material and realize the formability of material using in the process. Furthermore, they could understand when the undesired phenomena occurred during the forming process. Normally, the tensile test has been used to determine the characteristic of the material because this method was easy and cheap. However, the drawback of this tensile test is the leak of reasonable result because the specimen was deformed in only one direction, which is not coherence to the real forming process. In the practical process, the deformation of material was complicate and required the suitable experiment to describe the phenomenon of metal forming. Therefore, this research studied the formability of sheet metal by hydraulic bulge test. The sheet metal used in automobile industries was employed. The circular specimen was installed on the hydraulic bulge test machine, and the hydraulic system provided the pressure to form the specimens into the dome shape. Then the height of the dome was continuously increased until it broke. Based on this experiment, the dome height and forming pressure were used to characterize the relationship of stress and strain of material. The results obtained from this study revealed that the characteristic of material was more reliable and coherence to the sheet metal forming process.