Blends of polycarbonate (PC) with ABS and polycarbonate with maleic anhydride grafted ABS (MABS) were prepared by melt blending, using a single-screw extruder with special mixing head over the whole range of compositions. The rheological behaviour was determined using a capillary rheometer. The melt viscosity-composition curves for PC/ABS blends showed negative deviation from the rule of mixture with minimum values over a wide range from 25 to 65 wt.% PC. These curves for PC/MABA also showed negative deviation, but the deviation is less than that for PC/ABS blends. Addition of ABS or MABS to PC improves the processibility. Morphological studies of these blends were done using a scanning electron microscope (SEM). Morphology of unmodified blends showed coarse dispersion, whereas that of the modified blends showed fine and lamellar dispersion.Blends of polycarbonate (PC) with ABS and polycarbonate with maleic anhydride grafted ABS (MABS) were prepared by melt blending, using a single-screw extruder with special mixing head over the whole range of compositions. The rheological behaviour was determined using a capillary rheometer. The melt viscosity-composition curves for PC/ABS blends showed negative deviation from the rule of mixture with minimum values over a wide range from 25 to 65 wt.% PC. These curves for PC/MABS also showed negative deviation, but the deviation is less than that for PC/ABS blends. Addition of ABS or MABS to PC improves the processibility. Morphological studies of these blends were done using a scanning electron microscope (SEM). Morphology of unmodified blends showed coarse dispersion, whereas that of the modified blends showed fine and lamellar dispersion.