Blends of polycarbonate (PC) with poly(butylene terphthalate) (PBT) were characterized using density measurements, DSC, IR, and TGA. Addition of PET increases the density values of blends linearly. All the blends show a single glass transition temperature, indicating the miscibility of the two polymers in the amorphous phase. With more than 6% addition of PET to PC, PET crystallizes as per its own crystal structure. The addition of 4% PET to PC improves the thermal stability at higher temperature than does pure PC. IR studies shows that addition of PET improves the intermolecular forces in PC, in particular, on the endgroup and the C-CH3 and C=O groups as indicated in the frequencies 1020, 1370, and 1770-1790 cm(-1).