This study is focused on the characterization of polyethylene terephthalate (PET)/Styrene-Ethylene-Butylene-Styrene (SEBS)/Organomontmorillonite (OMMT) blends. SEBS-g-MA is used as compatibilizer and SEBS is the impact modifier at 30 %wt. The compounds were blended by twin-screw extruder and molded for test specimen by injection molding. The effect of OMMT types (Cloisite15A and Cloisite30B) and contents (1 and 3 %w/w) on properties of PET blends with SEBS and SEBS-g-MA were investigated. The PET composites incorporated with Cloisite15A had higher impact strength and %elongation at break whereas lower tensile strength than the one with Cloisite30B. Comparing with PET/SEBS/SEBS-g-MA blends, adding OMMT into PET/SEBS/SEBS-g-MA would increase thermal property. However, it had no significant changes with higher OMMT. %Crystallinity of PET would be increased with OMMT contents. PET/SEBS/SEBS-g-MA had lower %LOI but higher burning rate compared with PET. However, the addition of OMMT could improve flame retardant properties of PET blends. Addition of Cloisite15A and Cloisite30B into PET/SEBS/SEBS-g-MA increased %LOI. From UL 94 tests, polymer composites could be classified in HB class. The burning rate of polymer composites was decreased with increasing OMMT due to decomposition of OMMT act as a barrier to inhibit combustion.