Abstract: The effect of phosphate ester(PX-220) and its flame retardant synergism with Montmorillonite(MMT) on the flame-retardant properties and mechanical properties of recycled PET(rPET) and PC alloys was investigated by means of limiting oxygen index, mechanical properties testing, thermo-gravimetic analysis and scanning electron microscopic observation.The results showed that adding only 15% phosphate ester into the rPET / PC alloy, the oxygen index was up to 27%, and its oxygen index further increased to 29% when 2% MMT and 15% PX-220 was simultaneously used to fill rPET / PC alloy.However, there was an obvious decrease in mechanical properties.The thermo-gravimetic analysis indicated that the initial decomposition temperature of flame retardant materials modified with PX-220 and MMT together was lower than that of rPET / PC alloy without flame retardants, and that the thermal weight loss rate reduced after thermal weight loss was about 20% and the final char residue increased significantly.SEM images displayed that char residue layer was more integrated and dense to cover the burning surface of flame retarded material.