An device is for electron-beam irradiation sterilization of flexible bags that may contain human plasma protein solutions for therapeutic use. The device has two electron accelerators, a first accelerator emitting an electron beam with energies between 400 and 500 keV and a second accelerator emitting an electron beam with an energy of at least 4 MeV. A sterilization method by electron-beam irradiation provides sterilization of such flexible bags. An in-line filling process for flexible bags can use the sterilization device and method.