To meet societal and economic expectations, the bio-based composite market is developing. However, some issues remain, especially for lignocellulosic fiber composites, due to their highly hydrophilic nature which impacts the composite performance. This study focuses on bamboo fiber-polypropylene composites manufactured by film stacking using fiber mats obtained through a wet laid process. To individualize fibers, raw bamboo was cooked using an alkaline treatment: the soda process, i.e., using NaOH in order to keep a certain amount of lignin on fiber surface. A maximum surface lignin content of 81.%, measured by XPS analysis, was obtained, from the 1 wt.% NaOH concentration. The corresponding bulk lignin content, measured by Klayson method, is 21.%. The macroscopic properties of bamboo fiber-polypropylene composites were evaluated with regard to material microstructure through a multiscale analysis. The best mechanical properties were obtained for composites manufactured from bamboo fiber prepared using a 1 wt.% NaOH, which corresponds to the highest lignin content (3.5 GPa and 53 MPa for modulus and strength in tensile tests, 3.8 GPa and 64 MPa in bending tests). The good mechanical performance of the composites was attributed to the improved compatibility between the fiber and the matrix, evidenced by multiscale studies.