A novel graft copolymer, hydroxyethylcellulose-graft-poly (4-vinylpyridine), used as a physically adsorbed coating of the fused-silica (FS) capillaries, was synthesized by using ceric ammonium nitrate initiator in aqueous nitric acid solution. EOF measurements showed that the above graft copolymer coating of the FS capillaries could suppress EOF effectively compared with the bare FS capillaries. The adsorbed coating exhibited minimal interactions with proteins, providing efficient protein separations with excellent repeatability. Interestingly, the electrical charge of the coated capillary wall could be modulated by varying the pH of the running buffer, which makes possible the analysis of basic and acidic proteins in the same capillary. The effects of pH on suppressing EOF and protein separation were investigated in detail. The results demonstrated that the hydroxyethylcellulose-graft-poly (4-vinylpyridine) copolymer coatings have great potential in the diagnosis and proteomics.