The water bamboo husk is one of major agricultural wastes in Taiwan. In this study, the fiber and powder obtained from the water bamboo husk were chemically modified by coupling agents. Furthermore, the modified fiber and powder were added to the biodegradable polymer poly(butylene succinate) (PBS) separately, to form novel fiber-reinforced composites. Morphologies, mechanical properties, and heat resistance of these water bamboo husk-reinforced composites were investigated. The results indicate that the fibers modified by coupling agents exhibited better compatibility with the polymer matrixes than did the untreated fibers. Moreover, it is found that the thermal properties were improved as plant fiber was incorporated to those polymers. Furthermore, the mechanical properties were also increased with the addition of coupling agent-treated fiber. On the other hand, it is found that the homogeneity of untreated powder-containing samples is better than that of untreated fiber-containing samples. Moreover, the results reveal that the powders modified with coupling agents were not effective in improving the mechanical properties of the reinforced PBS. This is due to the bulky structure of lignin leading to a smaller reaction ratio with the coupling agents. (c) 2005 Wiley Periodicals, Inc.