The procedures for the production and the orientation of long fibers from Nypa fruiticans petioles were developed in our study. The unidirectional (UD) composites based on Nypa fruitican fibers and polypropylene (PP) were produced. The processing conditions such as fiber volume fraction, processing temperature were investigated respectively. In order to enhance the interfacial stability of the obtained composites, chemical treatment on fibers and matrix were carried out. Fibers were respectively treated with alkali, acetylation, silane. On the other hand, PP was treated with maleic-anhydride grafted PP (MAPP). The mechanical properties of these treated composites were observed and compared to figure out the optimum condition. In addition, chemical properties of fiber and composites were determined to explain the results.