The effects of various brominated flame retardants were investigated in PC/ABS blend system. The compatibilities between polymers and flame retardants were expected with the solubility parameter using group contribution theory. Tetrabromobisphenol A carbonate oligomer, among the flame retardants in this experiment, has been shown good miscibility for PC and ABS respectively. But polydibromophenylene oxide and octabromodiphenyl oxide has immiscibility. The flame retardant PC/ABS blends containning tetrabromobisphenol A carbonate oligomer have been exhibited higher mechanical properties, tensile strengths and notch Izod impact strengths, at various content of flame retardants, than containning other flame retardants. It could be seen that the trends of mechanical properties for the flame retardant PC/ABS blends have a good coinciclence with the expectation of compatibility.