In this study, the water hyacinth was used as a reinforcement of green composites. The chemicals for treatment of water hyacinth are solutions of alkaline, soap and water to determine water absorption. The chemical treated process of the water hyacinth fibers had important influences to the chemical structures and mechanical properties of the green composites. Micrographs analyses of scanning electron microscope (SEM) show obviously roughness of fiber surface after the chemical treatment as well as arrangement of structures among the water hyacinth fibers. Similarly, the results of analysis by Fourier transform infrared spectroscopy (FT-IR) showed that most of the intensity of the absorbed peaks was decreased markedly at the wavenumbers of 1375 cm-1 and 1542 cm-1. These are related to lignin extraction with alkaline solution, effectively. In particular, the compressive strength of the water hyacinth/roving composite has high value approximately to that of fiberglass composites (unfriendly composites). The water hyacinth/roving composites have significantly improvements in flexural and compressive strengths and this proves that the environmentally friendly composite responded to high requirements for various applications.