The synergistic effects of organically modified montmorillonite (o-MMT) and magnesium hydroxide (MH) on the flame retardance and mechanical properties of a thermoplastic-Vuldanizate (TPV) have been investigated. The incorporation of more than 6 phr o-MMT induces a drastically decreased peak heat :release rate and smoke production rate while simultaneously enhancing the mechanical properties of the TPV/MH composites. The improvements' in both flame retardance and mechanical properties are attributed to the double role of o-MMT in. the composites. On the one hand, the increase in viscosity due to o-MMT suppresses the vigorous bubbling caused by polymer pyrolysis. On the other hand, well dispersed o-MMT serves as a rigid network that prohibits massive shrinkage Of both the MH and TPV matrix during burning. Therefore, isolation of the protective chars by the clay network together with MgO is achieved, and such structure-prohibits-heat and mass transfer during burning.