Among the 85 lots of commercial cabbage seeds that were produced by 30 seed companies in Japan in 1988, three lots from three companies were found infested with s pathogen of black rot. The pathogen of black rot was effectively disinfected under a hot-air treatment: i.e. at 75℃ for 7 days for artificially infested seeds, and at 70℃ for 6 days or 75℃ for 2 days for naturally infested ones. No adverse effect on seed germination was observed under the treatment of 70℃ for 7 days, while the treatment of 75℃ even for 1 day prevented the germination. When the seeds were dried in advance at 40-70℃ for 24 hr, the germination rate was not lowered, even if those seeds were subsequently exposed to the temperature of 75℃ for 7 days. Pre-drying of seeds at 40℃ for 24 hr followed by an air treatment of 75℃ for 5-7 days is an effective method to disinfect cabbage seeds infested by black rot without any seed damage.