Amorphous polyamide (aPA)/acrylonitrilestyrene copolymer (SAN) blends were prepared using methyl methacrylate-maleic anhydride copolymer MMA-MA as compatibilizer. The aPA/SAN blends can be considered as a less complex version of the aPA/ABS (acrylonitrilebutadiene-styrene) blends, due to the absence of the ABS rubber phase in the SAN material. It is known that acrylic copolymer might be miscible with SAN, whereas the maleic anhydride groups from MMA-MA can react in situ with the amine end groups of aPA during melt blending. As a result, it is possible the in situ formation of aPA-g-MMA-MA grafted copolymers at the aPA/SAN interface during the melt processing of the blends. In this study, the MA content in the MMA-MA copolymer and its molecular weight was varied independently and their effects on the blend morphology and stress-strain behavior were evaluated. The morphology of the blends aPA/SAN showed a minimum in the SAN particle size at low amounts of MA in the compatibilizer, however, as the MA content in the MMA-MA copolymer was increased larger SAN particle sizes were observed in the systems. In addition, higher MA content in the compatibilizer lead to less ductile aPA/SAN blends under tensile testing. The results shown the viscosity ratio also plays a very important role in the morphology formation and consequently on the properties of the aPA/SAN blends studied. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 2540-2549, 2010