This work introduces the application of gray relation analysis as a multi optimization method in optimizing the machining parameters of face milling for hybrid Al-Si/Al2O3 /MWCNTs nanocomposites. The conventional vertical milling machine was used to carry out the experiments based on Taguchi orthogonal L27 array. Spindle speed, feed rate and depth of cut were considered as machining parameters. Surface roughness and flatness error were selected as a process response. The effect of various machining parameters was analyzed and the optimum combination of their levels were determined using both S/N ratio and ANOVA for gray relation grade. The results of this work showed that, the most significant parameter on multi-response was feed rate with contribution 26.34% followed by depth of cut with 19.99%. Also, the optimal levels of machining parameters are determined.