The effects of melt flow index (MFI) and acrylonitrile (AN) content of the styrene-acrylonitrile copolymer (SAN) on the mechanical properties and morphology of acrylonitrile butadiene styrene terpolymer were studied. A series of SAN had been blended with SAN graft polybutadiene rubber. The MFI of SAN matrix was varied from 6.2 to 84.7 gram/10 minutes and the AN content of SAN matrix was varied from 23.5 to 40.7%, while the AN content of the emulsion-made graft was fixed at 25%. The rubber content had been varied from 13 to 18%. The relationships between lzod impact and MFI of ABS with the MFI and AN content of SAN matrix and rubber content were proposed. Transmission electron photomicrographs showed similarity in rubber particle dispersion on 15.5% rubber content and SAN matrix containing 23.1, 29.3, 32.2 and 40.7% of AN content. However, as the difference in AN content of graft and the matrix increase, the rubber particle appear to be more agglomerated with large area of the matrix free of particles.