A thermoplastic molding composition containing polycarbonate, polyalkylene terephthalate and an elastomeric impact modifier is disclosed. The impact modifier that exhibits pH value of less than 7 and contains less than 500 ppm of sodium ions, is characterized in its core/shell morphology, where the core contains polymerized butadiene structural units and shell contains polymerized methacrylate structural units. The core is present in an amount of 40 to 70 percent relative to the weight of the impact modifier, and the glass transition temperature of the shell is greater than 23.degree. C. The composition is characterized in its improved surface quality and toughness at low temperatures.