In an attempt to prepare permselective membrane, grafting of acrylic acid (AAc) onto Teflon-fluorinated ethylene-propylene (FEP) film was studied in aqueous medium by the preirradiation method in air. Grafting was carried out by heating a mixture of AAc, water, and preirradiated Teflon-FEP film in air at 93 degrees C for definite time periods. Percentage of grafting was determined as a function of total dose, monomer concentration, reaction time, and amount of water. Maximum percentage of grafting (60.17%) was obtained at a total dose of 4.8 Mrad using 0.07M [AAc]. Evidence of grafting was obtained from the physical appearance and swelling behavior of the grafted film in polar solvents. Infrared spectroscopic and thermal analysis of the grafted film provided additional evidence for grafting. A plausible mechanism for grafting of AAc onto preirradiated Teflon-FEP film in air has been proposed.