The effects of a flame retardant (FR; reactive-type: brominated epoxy resin) on the mechanical and rheological characteristics of polycarbonate( PC)/acrylonitrile-butadienestyrene (ABS) blends were investigated at various conditions. A series of PC/ABS blends with and without the FR were prepared using a twin-screw extruder. The tensile yield strength and flexural strength of the blends increased with PC content, and the blends containing FR showed higher values than that of the blends without FR primarily due to the reactive nature of the FR. Furthermore, gradual increases in heat distortion temperature were observed over the broad range of PC content. The system without FR showed higher impact strength especially at high PC content. The temperature drastically affected the shear viscosity of the ABS matrix, but little changes in shear viscosity were observed for the PC matrix. This temperature dependence provided a characteristic viscosity change with respect to composition ratio in the blends. The relationship between shear viscosity and shear rate was analyzed using the Carreau model. The morphologies of the blends were also examined as a function of PC content. (C) 2003 Kluwer Academic Publishers.