Toughened polypropylene with balanced rigidity (TRPP) was prepared by thermal mechanical blending of PP resin with a toughening master batch (TMB) in a twin screw extruder. The dependence of the mechanical properties of TRPPs on the ratio of ethylene‐propylene to styrene‐butadiene elastomers, the total elastomer content in the TRPP, and the amount of elastomers in the TMB were investigated. The TRPP with a total elastomer content of 14 wt %, which was made from a TMB with 32 wt % elastomer and a 80/20 (w/w) ratio of ethylene‐propylene to styrene‐butadiene elastomers, was found to have excellent balanced mechanical properties. The notched Izod impact strength at 23°C was 762 J/m (23 times that of PP), the flexural modulus was 1078 MPa (92% of that of PP), and the tensile strength at yield was 34.8 MPa (88% of that of PP). Moreover, its mechanical properties were much better than the simply blended sample with the same composition, demonstrating that dynamic vulcanization and polymer‐bridge conjunction are excellent techniques to produce a high‐impact, high‐modulus PP. A sharp brittle–ductile transition was found at 14 wt % total elastomer content, which was assumed to be a percolation phenomenon. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1345–1350, 2001