Reversible addition-fragmentation chain transfer (RAFT) radical polymerization was used for controlled grafting of styrene and p-chlorostyrene from the surface of ramie fiber. The hydroxyl groups in ramie fiber were first converted to thiocarbonylthio groups as the RAFT chain transfer agent then used to mediate the RAFT polymerization of styrene, and p-chlorostyrene in tetrahydrofuran using azobis (isobutyronitrile) as initiator at 60 degrees C. The grafted copolymers were analyzed by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetry, and contact angle measurements. The results confirmed that grafting occurred on the surface of the ramie fiber, substantially increasing the water contact angle from 75.31 degrees to 147 degrees for polystyrene grafted ramie fiber (cell-PS) and 135 for poly(p-chlorostyrene) (cell-PSCl), and improving the hydrophobicity of the grafted fiber. The homopolymers formed in the polymerization were analyzed by size exclusion chromatography to estimate the molecular weights and polydispersity indices (PDIs) of chains grafted from the surface of the ramie fiber, as well as showed narrow chain length distributions with a PDI of 1.32-1.70. These materials possess potential applications in many advanced technologies. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 3551-3557, 2010