In order to develop polymer-clay nanocomposites with reduced flammability by incorporation of char-forming conventional nitrogen and phosphorus based flame retardants at low loading levels, the polypropylene-clay nanocomposites were prepared by melt blending method with Cloisite 15A (15A), organic phosphinate (OP) and ammonium polyphosphate (AP) additives. Thermal analysis shows that addition of 5% 15A along with 15% (w/w) OP in polypropylene (PP)/PPgMA increases the thermal stability of PP/PPgMA/OP/15A composite by 82 °C showing synergistic effect, and the PP/PPgMA/AP/15A sample with same loading becomes thermally stable by 70 °C. Cone calorimeter analysis of the PP/PPgMA/OP/15A and PP/PPgMA/AP/15A composites measures the reduction in peak heat release rate values by 66% and 58%, respectively. Addition of 20% OP to PP/PPgMA enhances the limiting oxygen index (LOI) value and gives V-2 rating of UL-94 test. Further, on replacing 5% OP with 5% 15A for PP/PPgMA/OP/15A sample without changing the total 20% loading, the LOI value increases further slightly but give no UL-94 rating. Also, PP/PPgMA/AP/15A sample with same loading similar to that of PP/PPgMA/OP/15A sample shows an enhancement in LOI value and gives no rating in UL-94 test. No relation was observed between LOI values and UL-94 test rating in the present study. Copyright © 2012 John Wiley & Sons, Ltd.