Natural hemp fibers were chemically modified using silane coupling agents to reduce their hydrophilic character. The existence of a chemical bond between coupling agents and hemp fibers was confirmed by ATR-FTIR spectroscopy, (29)Si Nuclear Magnetic Resonance (NMR), thermogravimetric analysis (TGA), energy dispersive spectroscopy (EDS), and BET surface area measurements. It was shown that the initial concentration and the chemical structure of the organosilane coupling agent have an effect on the grafted quantity on the hemp fiber surfaces. The grafted quantity increased proportionally to the initial concentration of silane molecules. The presence of polar amino end group (NH(2)) in silane structure can cause an increase in the grafted quantity, compared with results obtained in the case of silane molecules containing methacryloxy groups. This effect is attributed to the formation of hydrogen bonds between NH(2) and unreacted hydroxyl groups of hemp fibers. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 601-610, 2012