The polycarbonate / polyester (PC / PS) blend is one of the very distinctive blends which is distinct by its high degradation resistance and hence it is characterized by a good thermal stability. In the research in hand, we used X ray diffraction and UV spectroscopic methodologies to get information concerned with the influence of plasma (1 - 3 min.) on the structural and optical characteristics of the blend film. The changes of the optical band gap (Eg) and the refractive index (n) with the plasma exposure time were interpreted. An increase in n (1.5663 - 1.5764) associated with a reduction of Eg (6.71 - 6.58 eV) was noticed when we augment the exposure time up to 3 minutes. We assign these trends to the dominance of chain crosslinks. The plasma radiation encourages the transesterification interaction between the PC and the PS leading to a more compact structure of the copolymer.