Surface modification of free-standing polyaniline (PANi) films and PANi coating on low density polyethylene (LDPE) substrates via UV-induced graft copolymerization with hydrophobic monomers was carried out. Pentafluorostyrene (PFS) and styrene were successfully graft copolymerized on the PANi surfaces, rendering them hydrophobic. The effects of UV graft copolymerization time, graft copolymerization temperature, and monomer concentration on the graft concentration were investigated. The pristine and graft-modified films were characterized using both surface and bulk analytical techniques. For the pristine PANi films, the loss of counterions from the surface region of the film occurs very rapidly in deionized water. This loss is very effectively retarded by surface graft copolymerization with PFS, hence preserving the PANi＇s conductivity even upon prolonged immersion in deionized water. This enhancement in the electrical stability of the PANi film was also achieved in moderately basic aqueous medium.