As an index of viscosity, flowability of natural fibre polypropylene composites is assessed by spiral mould test using injection moulding machine. The effect of the processing parameters like the injection temperature at 180-220°C, injection pressure at 500-1000 bar and the mould temperature of room temperature and 80°C is studied. The investigated parameters are the fibre shape (Non branched straight cellulose versus low flexural stiffness and branched hemp fibres), fibre length (0.5 versus 1.5 mm chopped cellulose fibres) and fibre content Wf (10 versus 30 wt%). The results show that the most significant parameters in a descending order are the pressure, temperature and the mould temperature. Another aspect of the product quality is the homogeneity of the fibre content through the whole injected spirals. Therefore samples are taken out at even distances along the spiral. The cut samples are dissolved to extract fibres and calculate the fibre content. Fibre content definition along the injected spirals proved that it is not constant and the deviation in its measurements can reach to almost 30% from the nominal value. The results prove the separation of fibres before being injected specially in cases of low pressure and low injection temperatures. Secondly, the fibre content varies in a cyclic way. The number of cycles increases with the increase of temperature and pressure but with smaller amplitude of variation. The variation of the fibre content in cellulose fluctuates around an almost constant value which is not the case with hemp variation. Thirdly, the fibre content shows in most of the cases a parabolic trend with a minimum point just shortly after the input injection point. Fourth, the original fibre length affects the end product fibre content especially at both low pressure and temperature. Fifth, the variation in fibre content (Wfmax – Wfmin) along the spiral is clear in composites with hemp fibres at high processing temperature / pressure and vice versa, the composites of cellulose fibres show higher deviation at lower processing parameters. These results about variation in fibre content are studied in terms of the measured fibre dimensions. Fibre length is defined by the dynamic image analysis system QICPIC. Fibre length proves that the longer the fibre length, most likely the higher the fibre content. However, these results are still in need to be deeply analysed and better understood in order to open the door in future for robust simulation.