In automotive and transportation industry, it is essential to reduce the weight of vehicles for pollution and safety matters. To challenge this issue, a polypropylene reinforced with hemp fibers for injection molding, called NAFILean®, was developed by Faurecia to replace PP reinforced with glass fibers. In this study, we focused on filling and post-filling phases, which are highly dependent on the composite viscosity and its solidification temperature. Firstly, we realized that viscosity of such a material was dependent on fibers orientation. The viscosity characterization at low shear rates (from 0,001 to 0,1s-1) with a plate-parallel rheometer in continuous rotation mode showed a consequent increase at the beginning of the test as the fibers begin to rotate, the stabilization is observed at a strain around 5. These increase and stabilization can be explained by the building of a fibers aggregates system. Such microstructures would be difficult to break at these low shear rates, especially due to the combination of hemp fibers bundles and polarity difference between the fibers and PP matrix. Secondly, we showed that crystallization is highly induced by fibers and strain rate. The dependence on cooling rate and shear rate was experimentally observed by rheological tests. As strain-induced crystallization modelling could not be reasonably implemented without a non-linear viscoelastic constitutive model for the melt, we performed a solidification temperature depending on shear rate, which can be considered as a no flow temperature. Simulations of the injection process were performed with Moldflow® code. Simulation results were validated by comparing the sensitivity of viscosity and no flow temperature models on pressure and temperature evolution measurements from a specific mold. This will help us to reach the main purpose of this project which is predicting with accuracy shrinkage and warpage phenomena with simulation.