Quaternary ammonium compound 2-dimethyl-2-hexadecyl-1-methacryloxyethyl ammonium bromide (DEHMA) was synthesized and grafted onto polyester (PET) fibers with acrylic acid (AA) via electron-beam (EB) irradiation process. The grafted fibers were soaked in AgNO3 solution for further improving antibacterial efficiency. SEM, FTIR, EDX, and XPS were used to characterize the treated PET samples. The antibacterial efficacy testing showed the grafted PET samples inactivated all Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli O157:H7) in 10min. After coated with silver ions, the antibacterial efficacy of the grafted PET with silver against S. aureus improved significantly. The EB irradiation process only caused a small degree of the breaking strength loss of the grafted PET fabrics which is acceptable in practical application.