Currently, the ultralight steel auto body (ULSAB) concept is receiving more attention owing to various benefits in automotive body design. One of the tasks of the ULSAB is constructing a door using tailor welded blanks (TWBs). In TWBs, two or more gauges of steel panels (parts) are welded together before the stamping process. In this research, the domains and thicknesses of the gauges in a front door structure are determined by a series of optimization methods such as topology, size and shape optimizations and design of experiments (DOE). The door is designed to have better performance compared with an existing structure in terms of stiffness and natural frequency. The final design is discussed and compared with the current design.