A new method omitting oxygen removal procedures from polymerization mixtures was developed for graft polymerization of acrylamide (AAm) onto the surface of poly(ethylene terephthalate) (PET) film with the simultaneous UV irradiation method without photo-sensitizer. UV irradiation of the PET film with a high pressure mercury lamp under immersion in the 10 wt % aqueous solution of AAm containing an appropriate quantity of periodate (NaIO4) was found to give a highly hydrophilic surface with a water contact angle of about 20°. The original PET film had a contact angle of 75°. In the concentration range of NaIO4 below 1 × 10−4M and above 1 × 10−2M, polymerization did not take place, whereas polymerization was found to proceed to a significant extent when the NaIO4 concentration ranged between 3 × 10−4 and 5 × 10−3M. Based on the concentration change of O2 dissolved in the solution during polymerization and the UV spectra of the aqueous AAm solution containing NaIO4 exposed to UV radiation, a reaction mechanism was proposed for the graft polymerization conducted without degassing in the presence of NaIo4.