The modification of polypropylene (PP) with a combination of ethylene, propylene rubber (EPR) and glass fibres (GF) is a well known route to improving its mechanical properties. This is because the reductions in stiffness and strength due to the presence Of rubber particles are more than compensated by the addition of short glass fibres. This study has focused on the combined effects of glass fibres and rubber particles on the mechanical properties and mechanisms of deformation in PP-EPR-GF hybrid composites. Several composites with different amounts of rubber and short glass fibres were examined. To study possible synergistic effects, the total combined weight fraction of rubber and fibres was kept constant at 20%. The results of tensile tests show that the addition of glass fibres to PP EPR blends promotes yield strength and modulus while reducing elongation at break. Optical microscopy shows that, in the damage zones of all specimens, deformation bands. which appear similar to crazes, are visible after stretching. Scanning electron microscopy shows crazelike features including some voids, which tend to deviate from in plane propagation near the ends of glass fibres. The dominant mechanism of deformation in PP EPR GF observed in this work appears to be a crazelike type of damage, which is believed to be highly localised dilatational shear banding, propagating via repeated cavitation.