The effect of aminosilane on the properties of rice straw fiber (RSF) reinforced poly(butylene succinate) (PBS) composites was studied. RSF was pretreated with four different aminosilane coupling agents, 3-aminopropyltriethoxysilane (APTES), 3-aminopropyltrimethoxysilane (APTMES), 3-(2-aminoethylaminopropyl)triethoxysilane (AEAPTES), and 3-(2-aminoethylaminopropyl)-trimethoxysilane (AEAPTMES). The results of Fourier transform infrared spectroscopy (FTIR) and ? potential measurements confirmed that amino groups were introduced to the silane-treated RSF (TRSF) for all four silane coupling agents. The results also indicated a higher degree of hydroxyl ion adsorption by the fiber surface, which was chemically grafted by silane hydroxyl, was obtained with ethoxy silane than with methoxy silane. This difference might be because the relative rates of hydrolysis and ensuing silanol self-condensation of methoxy silane were too fast to reduce the number of silanol groups grafted on the fiber surface. The TRSF composite produced clearly enhanced tensile properties for the aminosilane coupling agents having ethoxy groups. The AEAPTES-RSF-PBS composite showed the highest tensile strength. It might be because of the higher amino content of AEAPTES than APTES; the amino groups on the surface of TRSF were confirmed by FT-IR to react with the carbonyl groups of PBS to form a blue-shifted hydrogen bond. The water absorption process of composites was found to follow the kinetics and mechanisms described by Fick's theory. The aminosilane treatment significantly reduced the moisture diffusion coefficient but did not change the mechanism of water adsorption. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012