Provided is an apparatus for sterilizing containers with a conveying device, which conveys the containers along a pre-set conveying path. A first sterilization device acts upon at least one area of the containers with radiation in order to sterilize them. A checking device is arranged downstream with respect to the first sterilization device along the conveying path in order to check the sterilization procedure. The checking device is used for analyzing at least one medium occurring in the region of the containers.