Melt-blended polysulfone (PSF) and poly(phenylene sulfide) (PPS) are notch sensitive. A significant improvement in the notched Izod impact toughness occurs when at least 10 wt% of a shell-core rubber modifier is incorporated into the blend. At rubber modifier levels above 15 wt%, the notched Izod impact strength was essentially retained upon annealing at 160-degrees-C for 2 h, while below 15 wt% of rubber modifier, the notched Izod impact strength decreases after annealing under the same conditions. Izod impact fracture surface morphology was studied using scanning electron microscopy (SEM). Fracture surfaces without a rubber modifier exhibit cavitation around the dispersed phase, i.e. PPS. On the other hand, fracture surface morphology of the rubber toughened blends with the same PSF/PPS composition show no cavitation surrounding the dispersed phase. Blend morphology was also studied using transmission electron microscopy (TEM).