The application of optimization technique in the frequency domain, to move the frequencies outside certain range, is presented. An engine cradle under development had very high responses in 50 - 60 Hz. range. A modal analysis identified the cause as the mounting springs' natural frequencies. Optimization technique (direct linearization method) was applied to change the spring stiffnesses to move its natural frequencies outside the range of interest. Response plots at various salient locations on the engine cradle, before and after optimization, confirmed the analysis. The large response in the frequency domain was moved outside the 50 - 60 Hz. range.