The hydrophobisation of commercial viscose-based activated carbon fiber (ACF) was obtained by grafting vinyltrimethoxysilane (vtmos) on the ACF surface, to improve ACF's adsorption selectivity towards carbon disulfide (CS2) under highly humid condition. The characterizations, including FTIR, Si-29 NMR, adsorption/desorption of nitrogen, thermal analysis and elemental analysis, revealed that the vtmos was successfully grafted onto the ACF surface, even though the hydrophobisation caused a partial filling of the porosity along with a slight decrease in the surface area. The efficiency of the hydrophobisation modification was evaluated by both equilibrium and dynamic adsorption experiment of water vapor and CS2. The equilibrium adsorption results indicated that the hydrophobisation modifications accounted for a decrease of both the amounts of water and CS2 adsorbed by the hydrophobised ACF. However, dynamic adsorption found that the adsorption performance was improved under highly humid condition, evidencing that hydrophobisation improved the hydrophobicity of the ACF surface and enhanced the adsorption selectivity towards CS2. (C) 2010 Published by Elsevier B.V.