Polycarbonate of bisphenol-A (PC)/copolyetherester (Hy) blends have been obtained by melt mixing over the complete composition range. After testing the lack of interchange reactions and degradation under the conditions studied, the miscibility state was studied by DSC and DMTA. The blends appeared to be miscible in the melt state. A fairly complex phase behavior was obtained in the solid state with T-g-composition plots showing a single T-g at most of the compositions but very different after the first and second scans. This was attributed to the different crystalline content of the blends before the two scans. The presence of a Hy crystalline phase and a single PC/Hy amorphous phase in all the blends, with the exception of the 20/80 composition, was verified by DMTA. Several thermal treatments showed the presence of an immiscibility range and, thus, the presence of a UCST. A LCST, which in the case of the 50/50 and 40/60 blends would be at roughly 75 degrees C, will also probably exist.