A new kind of zwitterionic molecule, [3-(methacryloylamino)propyl]-dimethyl (3-sulfopropyl) ammonium hydroxide inner salt (MPDSAH) was grafted onto polysulfone (PSF) ultrafiltration membrane surface using benzophenone (BP) as the initiator to improve the antifouling property. Polymer chain scission was suppressed by H-abstraction from methyl groups under long-wavelength UV irradiation (lambda > 300 nm), which avoided the photodegradation of PSF ultrafiltration membrane. The effects of MPDSAH concentration, UV irradiation time and BP concentration on grafting degree (GD) and the improvement of membrane antifouling properties were investigated, respectively. Attenuated total reflectance Fourier transform infrared spectroscopy (FTIR/ATR) and scanning electron micrograph (SEM) were used to characterize the chemical and morphological changes of the membrane surface. Static contact angle (CA) measurements showed that the hydrophilicity of MPDSAH-modified PSF ultrafiltration membranes was enhanced with the increase of grafting degree. The flux of pure water decreased slightly after modification, while the rejection to bovine serum albumin (BSA) increased. The improvement of antifouling property for MPDSAH-modified membrane was accordant with the increase of grafting degree. In addition, compared to PSF membrane, the modified membranes could maintain a higher water flux in wide pH range. (c) 2009 Elsevier B.V. All rights reserved.