Polypropylene (PP)/octene-ethylene copolymer (POE) blends were studied in both impact and high speed tensile tests, in which the practical strain rate was 208/s. With the increase of the POE content, brittle-ductile transition (BDT) of PP/POE blends occurred in both the impact and high speed tensile tests. BDT also occurred with the decrease of the tensile speed when any of the PP/POE blends was drawn. The impact deformation of the notched impact samples was analyzed in details. Most of the strain loading of the notched impact samples is taken by the deformation of the narrow region near the notch tip in impact tests. The microunits of the deformation region deform in two methods: high speed tensile deformation and shear deformation because of the tensile speed gradients in the deformation region. At the beginning of impact tests, the strain rate at the notch tip reaches almost 6000/s. In rubber toughened plastics, the shear deformation decreases greatly because of the rubber particle cavitation. Thus, the impact deformation is really a high speed tensile deformation at the narrow region near notch tips. The BDTs in both impact and high speed tensile tests share the same mechanism. The notch sensitivity of plastics is essentially the tensile speed sensitivity of plastics. (C) 2003 Elsevier Science Ltd. All rights reserved.