The effects of boehmite (BM) and vermiculite (VMT) on flame retardancy, combustion behavior and thermal degradation behaviors of polyethylene terephthalate (PET), BM/PET, and VMT/BM/PET composites were investigated by methods of limited oxygen index (LOI) measurement, vertical burning test, cone calorimeter test and thermogravimetry analysis (TG). The results showed that BM can effectively flame retardancy PET, when 12% BM was added into PET, 12-BM/PET composite possessed LOI value of 32.4% and V0 rating (3.2 mm) in UL-94 test. The flame retardancy, thermal stability and combustion behavior data of 2.5-VMT/BM/PET composite were better than that of 12-BM/ PET composite, indicates that appropriate amounts of VMT and BM in PET had synergistic flame-retardant effects. Replace part of BM with VMT, with the increased of VMT substitution amount, the flexural strengths and tensile strengths of VMT/BM/PET composites increased at first, and then decreased, the flexural modules was increased and the notched izod impact strength was decreased.