There is described a sterilization apparatus (1) for sterilizing receptacle closures (2) comprising a treatment chamber (4)； feeding means for feeding receptacle closures (2) to the treatment chamber (4)； guide rails (22) for guiding the receptacle closures (2) through the treatment chamber (4) and the feeding means feed the receptacle closures (2) to one active guide rail (22)； sterilization agent injection means (9) having injection devices (32), each associated to one guide rail (22)； and control means (50) for selectively actuating the injection devices (32) according to a first and second operative mode； in the first operative mode, the control means (50) actuate the injection device (32) associated to the active guide rail (22)； and in the second operative mode, the control means (50) actuate the injection device (32) associated to the active guide rail (22) and to one or more guide rails (22) adjacent to the active guide rail (22).
