The aim of this work is to reduce the flammability of polypropylene (PP) materials which are plenty used in a variety of industrial applications. For the first time, the efficiency of eco-friendly and low-cost flame retardant of CNTs prepared from rice straw on the flammability degree of PP/MMt composite is reported in this study. Mixtures of polypropylene/ montmorillonite /carbon nanotubes (PP/MMt/CNTs) were prepared by using different percentages of MMt and CNTs. The used CNTs sample was prepared from rice straw waste and the MMt was collected from Wadi El Hamadia, Egypt. The prepared samples were characterized by using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM), while the flammability properties were measured by using Limiting Oxygen Index (LOI). The results of FTIR and the photos of SEM showed that the MMt/CNTs composition is incorporated into the PP matrix. The LOI test revealed that LOI value of PP increased from 18.8% to 21.5 % in presence of MMt particles while the addition of 0.05 and 0.1 % of CNTs to PP/MMt significantly improved the LOI value to become 22.4 and 23.5%, respectively. This finding indicates that the addition of CNTs as co-nanofiller can improve the flame retardancy of PP/MMt composites. Thus the obtained MMt/CNTs composites act as synergist fillers to offer admirable and fire safe PP products.