Abstract.The synergistic effects of methylphenyl-polsiloxane solid powder and organophosphate flame retardant for polycarbonate (PC) were investigated by limiting oxygen index(LOI), and cone calorimeter. It was found that the LOI of the flame-retarded PC (FR-PC) with polysiloxane and organophosphate binary flame retardants didn't increase in comparison with that of FR-PC containing a single species flame retardant. The cone calorimeter results show that the heat release rate (HRR) of the PC/polysiloxane/organophosphate(PX230) composition is approximately 50% lower than that of the PC/polysiloxane or the PC/PX230. Total heat release (THR) of PC/polysiloxane/PX230 also significantly reduce in comparison with that of PC/polysiloxane and PC/PX230 binary composites, which indicates a clear synergistic effect of the polysiloxane and PX230 in the PC flame retardant composites. The CO production rate of the PC/polysiloxane/PX230 during combustion is slightly lower than that of the virgin PC. So the combination of the polysiloxane with PX230 used in PC could synergic inhibit the combustion heat release, and achieve environmental friendly fire-retardant effect.