f. is an important plant pathogen in tobacco-grown area of Weifang region of Shangdong Province, China. In this study, the toxicity of liquid culture media from different isolates was characterized, and some properties of the toxic ingredient were identified. The results indicated that the optimal toxin-producing conditions for f. were in potato dextrose broth under pH 6.0, at 25 similar to 30 A degrees C for 13 days. The liquid culture media from all isolates were toxic to tobacco plants and induced the wilting symptoms. The toxin from the liquid culture media has thermal, acid-base stability and a broad spectrum of toxicity to the plants. Furthermore, the direct bioassay for two components of the liquid filtrates precipitated by ethanol showed that the active ingredient of the toxin is a kind of nonprotein substance, which was further supported by the papain hydrolysis test.