Membranes have an increasingly important niche in the isolation and purification of biomolecules. In this work, a strong cation exchange membrane with high capacity was prepared via surface-initiated atom transfer radical polymerization (SI-ATRP). An initiator was first anchored to the surface of a regenerated cellulose (RC) membrane, and then poly(sodium 4-styrenesulfonate) (poly(NASS)) was grafted onto the surface of the membrane via SI-ATRP, affording an ion exchange membrane with the sulfonate as the exchange group. The grafting degree was controlled by varying the ATRP reaction time. The results from attenuated total reflectance Fourier-transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) indicated that poly(NASS) was successfully grafted onto the membrane. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrated that the surface morphology exhibits a significant change as a result of the grafting reaction. The water flux measurement illustrated that the surface modification decreased the pore sizes of the membrane to some extent. Lysozyme was used as a model protein to evaluate the adsorption properties of the modified membranes under static and dynamic conditions. The results demonstrated that the protein adsorption capacities increased with increasing ATRP reaction time and could reach a maximum capacity of 138.3 mg/mL and 92.9 mg/mL for static and dynamic adsorption, respectively. (C) 2012 Elsevier B.V. All rights reserved.