To increase the moisture content of polyacrylonitrile (PAN), thin layer surface photo-grafting of 2-hydroxyethyl methacrylate(2-HEMA) onto PAN fiber by using benzophenone as an initiator with a mixture solvent was carried. The effects of reaction conditions such as monomer and initiator concentration, UV irradiation time, composition of mixed solvent and immersion time of fiber on grafting were investigated. The percent grafting increased with increasing monomer concentration, benzophenone concentration, immersion time and UV irradiation time up to limiting value and thereafter decreased or leveled off. Using suitable mixed solvent significantly increased the percent grafting.