In this study, rice straw (Oryza sativa L.) fibril and fibril aggregates (RSFs) material isolated by high intensity ultrasonication (HIUS) was used as reinforcement in an RSFs/Polypropylene (PP) nanocomposites. The morphology of RSFs was investigated by scanning electron microscopy (SEM). The mechanical properties were evaluated by tensile test. The fourier transform infrared spectroscopy (FTIR) test was also performed to investigate the interface compatibility between RSFs and PP matrix. Results indicated that the tensile strength of RSFs/PP nanocomposites increased with increasing cycle time of extruder from 10 min to 30 min at 180°C. The maximum value of tensile strength was 31.2 MPa appeared at the conditions of 190°C and cycle 20 min. The elastic modulus increased by adding 5 wt% RSFs into the PP/MAPP matrix. However, there was no distinct difference of elongation in RSFs/PP nanocomposites at different extruder conditions. The RSFs embedded into the PP/MAPP matrix and exhibited better interaction by FTIR test.