The quality loss caused by tolerance of factors can be reduced when the nominal values of design-factors are carefully chosen. Therefore, the parametric optimization method is significant to an optimally define the Quality Loss cost (QLc). In this work, the Design Exploration (DE) and Taguchi Methods along with unforced Rotordynamic analysis have been used to find the optimal levels of factors affecting the QLc. Under definite constraints, the mathematical models are developed for an optimization problem and then utilized to develop Machine Motorized Spindle (MMS). In order to find the optimal levels of the factors, the sensitivities of factors on structural weight and First-Order-Nature-Frequency (FONF) has been analyzed using Response-Surface (RS) method, while the Taguchi method is used to find the QLc. The results found shown that there are significant enhancements in signal-to-noise ratio for structural weight and FONF. The QLc has been saved to about more than half-time by comparing to its initial values. The results also indicated that the proposed optimization approach is feasible and successful in improving dynamic characteristics and QLc saving for the MMS. Keywords: Machine Motorized Spindle, Finite Element Method, Unforced Vibration, Rotordynamic Analyses, Response Surface Method, Taguchi Quality Loss cost.