Due to their high mechanical properties along with high reinforcing capacity, cellulose nanocrystals (CNC) could be the ultimate choice for polymer nanocomposites as filler. Recently, different strategies have been reported for the processing of CNC reinforced polymer nanocomposite by extrusion method since it is a solvent free process and also this technique is most viable for commercial industrialization. However, sulphuric acid-prepared CNC limits the processing due to surface sulphate groups degradation because most polymers are processed at high temperatures. In this study we profitably used these negatively charged groups and CNCs have been modified with quaternary ammonium salt by a simple aqueous method and its surface adsorption was proved by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), x-ray diffraction(X-rd) ,contact angle, zetasizer and rheology measurements. The Modified cellulose nanocrystals (M-CNC) were extruded with polypropylene at 190°C and the ensuing composites were characterized to understand the mechanical, morphological properties by means dynamic mechanical analyser (DMA), deferential scanning calorimetry (DSC), tensile test and scanning electron microscopy (SEM).The dispersion of M-CNC in polypropylene matrix was studied by means of melt rheology and its reinforcing mechanism was described.