Ultrafiltration (UF) is one of the most widely used membrane technologies for the effective separation of macromolecules in feed solutions. However, despite good separation efficiency, the UF membranes made up of pure polymers suffer to a greater extent because of low flux problem, which affects the process time and load. To handle this limitation, the base polymer is blended with a suitable additive to modify the structural and surface morphology of the membrane to provide better fluxes. In this current study, a series of polyethersulfone (PES) UF asymmetric membranes blended with polyethylene glycol and iron oxide nanoparticles was prepared using the phase inversion technique. Prepared membranes were analyzed for their morphology, thermal stability, and membrane characterization. Morphology studies using scanning electron microscopy and atomic force microscopy confirmed the increase in the number of pores, pore size in support layer, and surface roughness in the blended membranes, ensuring the chances of enhanced flux. Surface hydrophilicity was increased with the increase in the iron oxide concentration in the composite membranes. Thermal analysis studies showed the better thermal stability of the blended membranes. Pure water flux of the prepared composite membranes was improved to a maximum of four times in comparison with pure PES membrane. Dye rejection studies clearly showed that the blended membranes almost had the same rejection as that of pure PES membrane. Thus, the prepared PES composite UF membrane is a promising candidate for the treatment of dye-polluted wastewater, ensuring high fluxes and effective rejection.