Hydrous manganese dioxide (HMO) nanoparticles were synthesized and incorporated in polyethersulfone (PES) to fabricate nanocomposite mixed matrix membranes (MMMs) for ultrafiltration (UF). The resulting membranes were characterized by XRD, FTIR, contact angle goniometer, SEM and AFM before further subjected to water permeation test and UF of bovine serum albumin (BSA) solution. It was found that contact angle of membrane decreased remarkably while porosity increased with an increase in HMO nanoparticle loading. The pore size at the skin layer however decreased as observed both by SEM and AFM. As for the UF experiments, pure water permeation rate increased remarkably with increasing nanoparticle loading but the permeation rate of BSA did not increase very much. Interestingly, the membrane flux recovery by washing with DI water was considerably enhanced by an increase in nanoparticle loading, indicating the improvement in membrane anti-fouling property upon HMO nanoparticle addition. The observed phenomena can be explained by the increase in membrane hydrophilicity and the formation of patterned surface with an increase in nanoparticle loading. (C) 2013 Elsevier B.V. All rights reserved.