Multi-stage hot forging is a typical manufacturing technology to produce mechanical components. In the forging, flash should always be minimized for material saving, and the uniform deformation is preferable for high strength of a product. The process parameters such as billet shape, billet temperature, die temperature, and stroke have also an influence on the flash and the uniform deformation. In this paper, the billet shape and the process parameters in multi-stage hot forging is optimized so as to minimize the flash and the equivalent strain. The numerical simulation is so intensive that sequential approximate optimization using radial basis function network is adopted for the design optimization. It is found from the numerical result that the flash is drastically reduced compared to the conventional billet shape. The smooth flow line can also be obtained with the optimal process parameters, and it is expected that high strength product will be produced.