Reinforcing thermoplastic polymers with short natural fibers improves mechanical properties and lightens produced parts compared to glass fiber reinforced polymers. Moreover natural fibers are renewable. Glass fiber length and orientation in molded parts is well known and has been quantified. The situation is much more complex with natural fibers because of various fiber composition and shapes (thick and stiff bundles or thin flexible elementary fibers). The objective is to analyze the microstructure of natural fibers in a molded part. Two types of fibers were used: flexible man-made cellulose fibers (Tencel®) and “semi-rigid” flax fibers. Fibers were mixed with polypropylene at different concentrations from 5 to 30 wt% in a twin screw extruder, pelletized and injected in a box shape mold. Fiber microstructure was quantified by optical microscopy and image analysis at different depths in the thickness. Fiber breakage increases with the fiber content. For flax, length and diameter reductions (separation of bundles into individual fibers) take place. Fibers were characterized by distinguishing 4 categories: rigid bundle, single wave and 2-wave curved fibers and fibers perpendicular to the observation plan. Percentages in each category, main axis or end-to-end vector orientation were quantified. Concerning orientation, fibers are slightly oriented perpendicular to the flow direction in the core of the molding, with a value of the orientation tensor component with respect to this direction in the range 0.2-0.5, whereas in the surface fibers are mostly oriented in the flow direction, with a value around 0.8. These results are related to shear and elongation flows experienced by the material during processing. The work is performed in the frame of the Industrial Chair on Bioplastics, organised by CEMEF/Mines ParisTech and supported by Arkema, L’Oreal, Nestlé, PSA, Schneider Electric. We thank Lenzing for providing Tencel® fibers and Ecole des Mines d’Ales for compounding.