We studied tensile behavior of low-molecular-weight (MW) polypropylene (PP)/ethylene-propylene rubber (EPR; 70/30) blends from the viewpoint of the MWs of PP and EPR and the compatibility between PP and EPR. The value of the melt flow rate of PP varied from 30 to 700 g/10 min at 230 degreesC. We studied the compatibility between PP and EPR by varying the propylene content in EPR (27 and 68 wt %). At the initial elongation stage, crazes were observed in all blends. When blends included EPR with 27 wt % propylene, the elongation at break of the low-MW PP improved little. The blends with EPR and 68 wt % propylene content were elongated further beyond their yielding points. The elongation to rupture was increased with increasing MW of EPR. Molecular orientation of the low-MW PP was manifested by IR dichroism measurements and X-ray diffraction patterns. The blends of low-MW PP and EPR could be elongated by the partial dissolution of EPR of high-MW in the PP amorphous phase. (C) 2002 John Wiley & Sons. Inc.