Blends of polystyrene (PS) and the polyether polyurethane elastomer (PU-et) were prepared by melt mixing using poly(styrene-co-maleic anhydride) (SMA) containing 7 wt % of maleic anhydride as a compatibilizer. The polyurethane in the blends was crosslinked using dicumyl peroxide or sulfur, The content of maleic anhydride was varied in the blends through the addition of different SMA amounts. The morphology of the blends was analyzed by SEM and a drastic reduction of both the domain size and its distribution was observed with increase of the anhydride content in the blends. The morphology of the PU-et blends also showed dependence on the crosslinker agent used for the elastomer, and larger domains were obtained for the clastomer phase crosslinked with dicumyl peroxide. The mechanical properties of the blends were evaluated by flexural and impact strength tests. The blend containing 0.5 wt % of maleic anhydride and 20 wt % of PU-et crosslinked with sulfur showed the highest strength impact, which was three times superior to the PS strength impact, and the blends containing 20 wt % of PU-et crosslinked with dicumyl peroxide showed the highest deflection at break independent of the anhydride content.