A series of charge-modified polyacrylonitrile (PAN) membranes with different surface charge properties and densities have been obtained via first grafting with hyperbranched polyethylenimine (PEI) and then ring-opening with 1,4-butane sultone. The obtained PAN-gr-PEI membranes and PAN-gr-PEIS membranes have hyperbranched polycation and hyperbranched zwitterions tethered on the surface, respectively. They were characterized in detail by FT-IR, AFM, XPS, SEM, WCA, and zeta-potential measurements. Bovine serum albumin (BSA) and lysozyme (Lys) were chosen as model proteins in order to evaluate the separation performance of the modified membranes via dead-end ultrafiltration. The membranes grafted with PEI of different densities have different surface chemical compositions but very similar surface charge properties. PAN and PAN-gr-PEI membranes are highly negatively charged and moderately positively charged. PAN-gr-PEIS membranes show typical amphoteric characteristics. The UF performance is highly dependent on charge prdperties. The membrane shows high flux and low transmission when membrane and protein have the same charge. At pH of 7 and 10, BSA and Lys are oppositely charged so that PAN-gr-PEIS and PAN membranes show good selectivity. When membrane and protein are oppositely charged, the membrane was fouled severely, including zwitterionic PAN-gr-PEIS membranes, which should be due to the stiffness of the hyperbranched zwitterions.