The morphology and the coarsening behavior with and without compatibilizer were investigated by using scanning electron microscope. As a new compatibilizer, styrene-acrylonitrile-maleic anhydride terpolymer (S-AN-MAH) was used. For Polycarbonate (PC)/Nylon6-co-12(50/50) blend, modulated structure was observed. And coarsening behavior was similar to that of spinodal decomposition. However, for PC/Nylon6-co-12(50/50) blend with S-AN-MAH, sea-island structure was developed and the size of domain did not increase although the sample was annealed for 90 min, at above T-m. It was confirmed that S-AN-MAH retards coarsening of morphology.