It is well known that improving NV performance and weight saving are reciprocity. Brake squeal free is one of the top priority issues during development of brake system. To date, complex eigenvalue analysis has been utilized for prediction of brake squeal. It solves the structural instability problems by modal coupling which is the phenomenon that natural frequencies of normal modes are quite consistent. The positive real parts of complex eigenvalues are identified as instable vibration which causes brake squeal. On the other hand, the needs for light-weight brake system are higher than before due to recent trends of economizing fuel consumption and high driving performance. In order to obtain coexistence of brake squeal free with weight saving, shape optimization technique has been proposed for complex eigenvalue analysis. In this study, the real parts of eigenvalues are shifted to stable side analytically by optimization algorithm using response curved surface with minimizing mass of a brake assembly. For simplified FEM model consisting of a rotor and a pad, thickness of backplate of brake pad is set as design parameter, mass minimization as objective function, and real parts of the eigenvalues are lower than zero as a constraint condition. Shape optimization technology, as mentioned above, achieves the lightweight construction with brake squeal free analytically.