The optimum design for a bow structure of high tensile steel yacht belongs to the nonlinear constrained optimization problem. The determination of scantling for the bow structure is a very crucial matter out of whole structural design process of a yacht. This determination may be a process of satisfying a lot of complicated design constraints empirically, rather than optimizing some objective function. However, in order to realize optimum or rational design for bow structure with complicated design constraints, it is necessary to model the design problem as strictly as possible and to accomplish more highly numerical optimization. Real-coded Micro-Genetic Algorithm is proposed to find the optimum scantling for the bow structure of high tensile steel yacht without handling any of penalty functions.