Characterization and application of ultrafiltration membranes are of great interest today, both as a tool in choosing the proper membrane for the filtration system used and in the development of new and better membranes. Cellulose acetate was blended with polyurethane in a polar solvent in the presence of polyvinylpyrrolidone as an additive. The effects of polymer composition and additive concentration on membrane compaction, pure water flux, water content, membrane hydraulic resistance and morphological studies were discussed. Measurement of transmembrane flux and appropriate macro solute rejection during stirred ultrafiltration of aqueous solutions of proteins and metal ions chelated with polyethyleneimine were carried out individually using CA/PU blend membranes.