There is a growing demand for commercial vehicles with a lightweight design due to fuel costs and environmental regulations. In this study, a bulk trailer is selected with the axle, suspension arm, and 5th wheel removed for simplification. Three extreme driving conditions when fully loaded are considered for the loading boundary conditions. Compliance minimization with a mass constraint is conducted in order to determine a lightweight design under these boundary conditions. Finally, based on the optimized design and consultation with field experts, a pilot model is determined and manufactured. This revised model can successfully achieve 14 % mass reduction in a bulk trailer compared with an original model.