In this work, tertiary polymer blends based on polypropylene (PP)/polycarbonate (PC)/poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) triblock copolymer and a reactive maleic anhydride grafted SEBS (SEBS-g-MAH) at fixed compositions are prepared using twin-screw extruder at different levels of die temperature (235-245-255 degrees C), screw speed (70-100-130 rpm), and blending sequence (M1-M2-M3). In M-1 procedure, all of the components are dry blended and extruded simultaneously using Brabender twin-screw extruder, whereas in M-2 procedure, PC, SEBS, and SEBS-g-MAH minor phases are first preblended in twin-screw extruder and after granulating are added to PP continuous phase in twin-screw extruder. Consequently, in M-3 procedure, PP and SEBS-g-MAH are first preblended and then are extruded with other components. The influence of these parameters as processing conditions on mechanical properties of PP/PC/SEBS ternary blends is investigated using L9 Taguchi experimental design. The responding variables are impact strength and tensile properties (Young's modulus and yield stress), which are influenced by the morphology of tertiary blend, and the results are used to perforin the analysis of mean effect as well. It is shown that the resulted morphology, tensile properties, and impact strength are influenced by extrusion variables. Additionally, the optimum processing conditions of tertiary PP/PC/SEBS blends were achieved via Taguchi analysis. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2312-2319, 2010