Thio-ene chemistry was used to modulate pore size and surface properties of regenerated cellulose membranes (RCM). A series of thiol PEGs (PEG-SH) (M-n, ca. 2000, 6000 and 10,000 g/mol) were tethered onto vinylated RCM surface. The membrane surface was analyzed by ATR-FTIR, XPS and SEM. The thio-ene reaction conditions, including the UV irritation time, the 2,2-dimethoxy-2-phenylacetophenone (DMPA) concentration and the PEG-SH concentration, were optimized to achieve high graft yields. The highest graft densities for PEG2000, PEG6000 and PEG10,000 are 1.37 nm(-2), 032 nm(-2) and 0.10 nm(-2), respectively. Membrane pore size was determined using the Guerout-Elford-Ferry method. The antifouling performance was evaluated by the protein filtration experiment. Effects of graft chain length and graft density on membrane morphology, pore size, permeation and antifouling properties were systematically studied. The results indicate that the change of membrane morphology, pore size and permeation properties with PEG grafting is more closely related to graft density than the chain length. The attainment of high graft density is more important than long chain length to achieve excellent antifouling performance. A series of membranes with pore size ranging from 70 to 140 nm were obtained. (C) 2013 Elsevier B.V. All rights reserved.