The tensile behavior

noteched Izod impact strength and the morphology of the impact fracture surfaces of ternary PS blends(PS／SBS／CaCO3) were investigated. Two kinds of CaCO3 fillers with micrometer and nanometer sizes were used．Its was found that the CaCO3 of micrometer sizes was a better toughness modifier than that of nanometer sizes

while the latter gave more improvement in the stiffness of the system．The toughness of the PS blends increases apparently with the increase of the SBS／CaCO3 content．A brittle-ductile transition was observed with increasing the SBS／CaCO3 content. All the results including the impact and tensile tests and morphological observations indicated the transition in the same content region of 31.0 wt％～37.5 wt％.