Tensile properties of both a binary material, i.e., polystyrene (PS) reinforced by 15 vol % of glass beads, and ternary composites, i.e., showing either a maleated styrene/ethylene-co-butylene/styrene copolymer or a styrene-co-methacrylic acid copolymer (SAMA) adduct at the PS/glass-beads interface, are analyzed at room temperature and over a wide range of strain rates. Because the poor quality of the adhesion at the PS/glass-beads interface, the fracture toughness of these binary composites is strongly reduced, whatever the strain rate. The presence of the rubbery interlayer does not change the deformation mechanisms of the composite and the work to break is not significantly enhanced. This results from the poor compatibility between PS and the rubbery interphase leading to the debonding of coated glass beads. The good adhesion quality at the interfaces between phases in the ternary composite showing the SAMA adduct, i.e., SAMA/glass-beads and PS/SAMA interfaces, hinders the decohesion phenomenon. This results in an improvement in both the transfer load and the maximum strength.