Two polybutadiene-graft-acrylonitrile-styrene copolymer (PBD-g-SAN) impact modifiers with different rubber particle size were synthesized by seeded emulsion polymerization. Acrylonitrile-butadiene-styrene (ABS) blends with a constant rubber concentration of 15 wt% were prepared by blending those impact modifiers and SAN resin. The major focus was the mechanical properties and deformation mechanisms of ABS blends under Izod impact test and uniaxial tension at various strain rates from 2.564 x 10(-4) S-1 upto 1.282 x 10(-1) S-1. By the combination of transmission electron microscope and scanning electron microscope, it was concluded that crazes and cavitation coexisted in ABS blends. The deformation mechanisms of ABS blend containing large rubber particles was rubber particles cavitation and shear yielding in the matrix including crazes, and they do not change with the strain rate. Different from ABS blend with large rubber particles, deformation mechanism of ABS with small rubber particles under tensile condition was only involved in shear yielding in the matrix and no crazes were formed. POLYM. ENG. SCI., 51:902-907, 2011. (C) 2011 Society of Plastics Engineers