An instrumented-drop weight impact test carried out at room temperature under a range of loading rates was applied to study the deformation and failure behaviors of PC/ABS (50/50) blends. Actually, these blends have different type of ABS, one grade of the blends is the blend containing small-sized particles of rubber and another grade is the blend containing larger-sized particles of rubber in the ABS systems. Testing results showed that both of the blends generally exhibited similar behaviors but they were totally different under 3 m/sec. A weld line-like formation captured on the fracture surface was found in each of the blends. Preliminary study using scanning electron microscope (SEM) indicated that crack also propagated along the weld line. Fracture of the blends might be initially induced due to fracture of the weld lines. Hence, it has been suspected as a factor affecting behavior of the blends. Since existence of the weld line-like formation has not been found in fractured ABS materials, it is necessary to point out the complex relationship among of the ABS composition, the existence of the weld line and the weld line quality in the blends. A finite element (FE) simulation of the testing was carried in order to determine whether the weld line strength is significant enough affects the behaviors. Although the model was generated using estimated failure criterion for the weld line, the simulation results showed that weld line strength might influence the blends behavior.