The miscibility of poly(ethylene terephthalate) (PET) with polyarylate (PAr), polycarbonate (PC), and poly(estercarbonate) (PEC), polyarylate-polycarbonate random copolymer were examined from thermal properties, and morphology. PAr, PC and PEC all showed phase separation behavior in blends with PET. On the other hand, as the carbonate/ester repeating unit ratio increases, the penetration of PEC into PET tends to increase, and the corresponding suppression of crystallization was observed. In SEM study, on the contrary, the apparent morphology was resulted in as if PET and PEC1 are more favorable, which is attributed to the fact that in morphology the control processing condition can be a dominant factor for immiscible blend systems