The stress-strain behavior of blends of nylon 6 (PA) and a styrene-acrylonitrile copolymer (SAN) compatibilized by an imidized acrylic polymer (IA) was evaluated in terms of the LA content and the dispersed SAN25 particle size. PA/SAN blends can be considered as a simpler version of industrially important PA/ABS blends; therefore, this study provides better understanding of the stress-strain behavior of compatibilized PA/ABS blends. The IA content was Varied from 0 to 5 wt%; whereas the ratio of PA to SAN25 was held at 7/3; and in all cases the polyamide formed the continuous phase. From experiments using a Brabender batch mixer or an extruder as the mixing device, a reduction of dispersed particle size was observed with the addition of as little as 0.1 wt% IA. It was revealed from the experiments using a Brabender batch mixer that more than 0.5 wt% IA was necessary to prevent domain coalescence. The blends containing I wt% or more LA show necking and considerable plastic deformation. Transmission electron microscopy revealed that the normally brittle SAN25 particles were transformed into elongated shapes and undergo shear yielding under certain circumstances as the specimens experienced plastic deformation during stress-strain testing. Although the macroscopic elongation at break and the particle distortion ratio, which is defined as the ratio of the major axis to the minor axis of the elongated particles, are somewhat correlated, the local deformation in the neck region is much larger than the elongation at break. Thus, the ultimate capability for plastic deformation of the IA compatibilized blends is much larger than the overall elongation at break. The distortion ratio of the particles was observed to be as high as 6-7. There seems to be a relationship between the SAN25 particle size and the extent of plastic deformation realized. These experiments, however, do not differentiate the effect of diminishing particle size from increasing adhesion between the phases. Thus, it is not possible to assign unambiguously the dominant factor that permits the plastic deformation of the brittle SAN phase. (C) 2001 Elsevier Science Ltd. All rights reserved.