Selected grades of polystyrene (PS) and linear low density polyethylene (LLDPE) are blended over the entire composition range and the mechanical and rheological properties of the blends evaluated. Styrene-ethylene-butylene-styrene (SEBS) block copolymer is found to be an effective compatibilizer for modifying the mechanical behaviour of PS/LLDPE blends. The blends are found to be sufficiently compatible in the molten state.