Poly(vinyl chloride) was blended with an acrylic rubber at a variety of blending ratio using a twin-screw extruder. The acrylic rubber was compounded with sulfur and sodium stearate in a two-roll mill prior to the blending. Dynamic vulcanization was performed in a compression mould at 170degreesC. Mechanical properties of the blends were determined by using a tensile testing machine. Scanning electron microscope was used to examine morphology of these blends. Degree of crosslinking of acrylic rubber in the blends was evaluated by using a differential scanning calorimeter. It was found that the normal blends are miscible regardless of the blending variables. By performing dynamic vulcanization, however, the blends became immisicible, showing a typical dispersed particle morphology, which was accompanied by a remarkable improvement of tensile properties. The screw-rotating speed was an important parameter affecting particle size and crosslink density of the rubber phase, which in turn controlled the tensile toughness of the blends. On the one hand, tensile toughness increased with the speed because of the decreasing particle size. On the other hand, the toughness decreased with the speed because of the decreasing crosslink density of the rubber. As a result, there was an optimum speed for each blend ratio, which corresponded to the maximum toughness. (C) 2003 Wiley Periodicals, Inc.