Poly(acrylonitrile-butadiene-styrene), polycarbonate (PC), and two types of antioxidants have been blended by an extruder twin screw. Notched Izod impact strength, tensile property, and melting flow index (MFI) were measured for the blends including different amounts of antioxidants, and morphology of the blends was investigated by scanning electron microscopy (SEM). The antioxidant action, especially on mechanical properties and the phase structure of the blends, has been studied for the undegraded samples. It was found that the phenolic antioxidant, tetrakis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyloxy-methyl) methane, C73H108O12, whose commercial name is KY-7910, and phosphite antioxidant, triphenyl phosphite (TPP), (C6H5O)3P, all decrease the Izod impact strength and tensile modulus of the blends and increase the elongation at break if a small amount of the antioxidants (such as less than 0.7%) was mixed into the blends. When the content of the antioxidants is increased, surpassing 0.7%, KY-7910 has little effect on impact property of the blends, but TPP made the Izod impact strength decrease and the MFI increase to a great degree. SEM results show that the two phases of ABS/PC with a weight ratio of 30/70 is cocontinuous; this structure is destroyed by addition of the two antioxidants, and in ABS/PC/antioxidants blends, the size of the ABS phase, as dispersion, does not change not much with increasing KY-7910 content, but becomes more scattered and greater with increasing content of TPP. These results are consistent with the mechanical tests.