The optimization of injection molding process for polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blends is studied using Taguchi method and principal component analysis (PCA). Four controllable process factors are studied at three levels each in the manufacturing process. The L9 orthogonal array is conducted to determine the optimum process factor/level combination for single quality of mechanical properties. In addition, the principal component analysis is employed to transform the correlated mechanical properties to a set of uncorrelated components and to evaluate a comprehensive index for multi-response cases. Then the optimum process factor/level combination for multiple qualities can be determined. Finally, the analysis of variance is used to find out the most influential injection molding parameter for single and multiple qualities problems.