The thermal behaviors of binary blends of polycarbonate (PC)/brominated polystyrene (PBrS) and ternary blends of PC/PBrS/poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) were investigated. The compatibilizing effect of PPO on the miscibility of the PC/PBrS blends was examined. The miscibility of binary and ternary blends was studied by using differential scanning calorimeter (DSC). The results of DSC indicate that the binary blends of PC/PBrS are immiscible but ternary blends of PC/PBrS/PPO in certain limits are miscible. The microstructural properties of the blends was characterized by environmental scanning electron microscope (ESEM) where the properties are determined in the natural state of the structural role of individual phases (PC/PBrS/PPO) and their effect on the overall microstructure of the products. DSC and ESEM results were supported by FT-IR measurements.