The effects of reprocessing on the processability of two Acrylonitrile–Butadiene–Styrene (ABS) grade thermoplastic polymers have been investigated. Reprocessing in an injection molding process of a low and a high viscosity ABS grade has been done changing operating temperatures and shear rates, design of experiments (DOE) techniques were applied to plan experiments and later analysis. The flow properties of virgin and reprocessed materials have been evaluated by capillary rheology. Experimental results clearly indicate a qualitatively different behavior of the two polymers upon reprocessing. Low viscosity grade shows a reduction of viscosity upon increasing the number of processing cycles, thus confirming the degradation of this polymer. High viscosity grade, conversely, shows an increase of melt viscosity as the number of injection molding cycles is increased. It has been confirmed that applied shear rates in injection molding process affect material behavior as well as applied temperatures.