Natural rubber-g-poly (styrene-co-acrylonitrile) (NR-g-SAN) copolymers were prepared by emulsion polymerization of styrene and acrylonitrile in NR latex and were melt blended with SAN to improve its impact resistance. The present paper reports the melt rheological behavior of SAN/NR-g-SAN as a function of rubber content in the blend, temperature, percent grafting of the graft copolymer and acrylonitrile content in the grafted chain. The melt viscosity of both SAN nad the blends at different rubber content decreased with increase in shear rate and shear stress confirming pseudoplasticity. At lower shear stress (3 x 10 4 Pa) and shear rate (<50s-1), the viscosity of SAN remained constant while that of the bleds showed a tendency to increase. The melt viscosity was higher at higher rubber content. At shear rates above 3200 s-1, the viscosity of the blends having various rubber content was similar. The activation energy at constant shear stress remained constant while that at constant shear rate decreased by increasing shear rate from 10s-1 to 100s-1 and then remained constant implying that rubber modified SAN is less sensitive to temperature changes at higher shear rates and shear stresses. At constant rubber content, acrylonitrile content in the grafted chain did not influence the melt viscosity of these blends while it was influenced by percentage grafting at lower shear rates and shear stresses.