A series of poly(ethersulfone) (PES) ultrafiltration membrane blended with poly(acrylic acid) (PAA) was prepared by phase inversion method by varying the PAA composition from 0 to 10 wt% in the polymer blend compositions. Prepared membranes were analyzed for their morphology, ultrafiltration (UF) characterizations and dye rejection performance. Cross-sectional morphology study using SEM showed the increased pore size of the sublayer of the asymmetric membranes due to PAA addition. AFM studies confirmed the enhanced surface roughness of the PES/PAA blend membranes. Surface hydrophilicity was increased with increase in the PAA concentration in the composite membranes. Porosity measurements confirmed the porous nature of PES/PAA blend membranes than the unmodified PES membrane. Pure water permeability of the PES/PAA blend membranes was improved to a large extent in comparison with pure PES membrane. Dye rejection studies revealed the decrease in rejection efficiency due to the PAA addition to PES matrix owing to increased pore size. Results obtained clearly indicated the better performance of 2.5 wt% PAA blend membrane in comparison with other synthesized UF membranes. © 2015, Sphinx Knowledge House. All rights Reserved.