This work is a continuation of the previous works by the authors to increase the effeciency of ammonium polyphosphate(APP) as flame retardant for polypropylene(PP). In this work a more abundant kaolin was used. Also to improve the effciency of kaolin, an acid modification by sulfuric acid was used. XRD, XRF, IR, SEM and BET were used to characterization the samples. TGA and DTA were used to evaluate the prepared samples as flame retardant. For comparison, six samples of (APP/ Ore kaolin)/PP were prepared and other six samples (APP/Modified kaolin)/PP have the same composition and identical to the ore kaolin were prepared. The analysis of the XRD, IR and SEM results indicate that the acid treatment of kaolin increases the SiO2 content which lead to increase the surface area. In the same time the acid leachig causes some destortion in the crystallinity and the layers. The evaluation of the flamability of the system by using the TGA indicate that the presence of kaolin increases the time of degradation of PP. On other hand, the modification of kaolin by sulfuric acid improves the role of the kaolin when added to the APP.