A comprehensive experimental study was carried out to investigate the effects of 1) viscosity ratio, 2) temperature on the viscosity ratio, 3) extruder screw location,. and 4) compatibilizers on the morphology of bisphenol-A-polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS). Blends were prepared by utilizing a co-rotating twin screw extruder and in-situ morphology obtained via the screw pullout technique. A plot of the PC/ABS viscosity ratio, eta(PC)/eta(ABS), versus the shear rate showed a gradual rise in the curve up to a critical shear rate and thereafter displayed asymptotic character. Contrary to premise, eta(PC)/eta(ABS) decreased with increasing temperature. This was elucidated by the melt viscosity of PC being thermally more sensitive than ABS over the temperature range investigated. As expected, the plot of the average domain size versus the viscosity ratio gave a concave up curve with a minimum when the viscosity ratio was close to unity. The morphology evolution along the screw of a twin screw extruder was examined. When sections of the kneading block were examined, the minor phase domains gradually showed reduction in size toward the extruder die, and the smallest domain was realized at the end of the block, namely, the flow impeding left-handed screw element. Polymethylmethacrylate (PMMA) exhibited the greatest ABS domain size reduction, and annealed samples showed that it suppressed coalescence.