Current research is actively devoted to the development of high-performance ultrafiltration membranes with high permeability at maximum selectivity for dedicated separations. This work reports the preparation of polymer blend charged ultrafiltration membranes for the improvement of fractionation selectivity. Flat sheet membranes made from polysulfone and various types of sulfonated poly(arylsulfone)s were prepared via non-solvent induced phase separation. Membrane morphology, hydrophilicity and surface charge were assessed by scanning electron microscopy, contact angle and zeta potential measurements, respectively. The separation performances, i.e. selectivity factor, permeability, and permeability recovery, were evaluated by ultrafiltration of model proteins - bovine serum albumin (BSA) and hemoglobin (Hb). Results showed that the membrane charge can be tuned by adjusting the fraction of sulfonated groups via the type of sulfonated polymer in the blend used for membrane preparation. Hence, a broad range of ultrafiltration membranes with different barrier pore sizes, permeability properties and surface charge was established. Pronounced differences between the effects of different types of sulfonated poly(arylsulfone)s at the same degree of sulfonation and mass fraction in the membranes had been found and related to different barrier structures formed during phase separation. Successful separation of protein mixtures was achieved by additionally adjusting filtration parameters. Overall, this work provides guidelines for a versatile and easy method to tailor membrane properties for the selective separation of binary mixtures of biomacromolecules with nearly identical molecular weight and potentially also to solve other separation problems.