Blends of a poly(phenylene oxide) (PPO) with high-impact polystyrene (HIPS) were injection molded. The static mechanical properties and fracture toughness of the blends were determined by means of the uniaxial tension, Brinell hardness and three-point-bending measurements, From the static mechanical test results, it was shown that the yield strength, Young’s modulus and hardness values oi the PPO/ HIPS blends were considerably higher than those of their PPO and HIPS component polymers, Dynamic mechanical measurements indicated that the PPO/HIPS blends appear to be miscible as shown by the existence of a single grass transition temperature. Furthermore, the J integral method based on ASTM E813-89 procedure was used to characterize the fracture toughness of PPO/HIPS blends. The J integral analysis indicated that the PPO specimen exhibited the lowest fracture toughness (J(c)), The PPO containing 50 wt% HIPS blend had the highest J(c). SEM observations revealed that the crack growth zone of the pure PFO is relatively smooth. However, cavitation of the elastomeric particles and shear band formation were observed in the deformed zones ahead of the crack tip of the PPO with 50 wt% HIPS blend. The cavitation and shear band formation mould dissipate bulk strain energy and their formation was responsible for the highest J,value observed in this blend.