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Natural fibre-reinforced composites have attracted great research and economic interests because of their outstanding green' characteristics compared with glass fibre-reinforced composites. It is very important to understand the processing effect on the natural fibre-reinforced composites mechanical properties because of the natural fibre degradation characteristics. Optimizing the fabrication process, especially the compounding process, is effective to achieve the optimal properties of the composites. In this research a natural fibre, noil hemp fibre, was applied to reinforce polypropylene with internal mixing process. The influence of compounding parameters, such as mixing temperature, mixing time and rotor speed, on the mechanical properties (tensile strength, flexural strength and impact strength) of the noil hemp fibre/polypropylene composites was investigated using orthogonal method and the evidence of thermogravimetric analysis test of fibre and the observation of fibre dispersion in resin. The range analysis and variance of analysis demonstrated that the mixing temperature has significant effect on the three mechanical properties, mixing time has minor influence on the tensile and flexural strengths, and rotor speed mainly affects the impact strength. The thermogravimetric analysis test of noil hemp fibre and the fibre dispersion in resin show that a combination of low mixing temperature, short mixing time and high rotor speed of compounding process is helpful to achieve certain fibre dispersion without serious thermal degradation of fibre. Noil hemp fibre/polypropylene composites with the best comprehensive mechanical properties could be obtained at 165? for 12min with rotor speed 50r/min.