Rheological behavior of polycarbonate (PC)polyester blends is studied. The miscibility and rheological behavior are discussed. Effect of catalyst, tetra-n-butyl orthotitanate on the transesterification reactions for a [60 (PC):40 (PET or PBT)] blend is studied rheologically. The blends were mixed for different spans of time for rheological study. The blends are analyzed on the basis of the mechanism suggested by other researchers. As the mixing time is increased, the blends show decrease in viscosity. Random copolymers also are amorphous in nature. (c) 2007 Wiley Periodicals, Inc.