Surface modification of microporous polypropylene hollow fiber membranes was performed by graft polymerization of acrylic acid. The effects of temperature, polymerization medium, monomer concentration and multifunctional cross-linker on the graft polymerization were studied. The grafting degree on the polypropylene membrane can be greatly increased upon the addition of divinylbenzene (DVB). Scanning electron microscopy (SEM) pictures demonstrated that PAA grafted mainly on the surface of the membrane. Mercury porosimetry analysis revealed that the grafting also took place within the pores. Contact angle and absorbed water measurements showed excellent wetting properties with water for the grafted membranes. The grafted membrane did not show high flux for ultrapure water because the grafting of AA plugs the pores of the membrane.