This paper presents discussions on the anaerobic fermentation products of distillers' wastes at the Fermentation Institute in Chiba Prefecture and the Yoshinoya Factory in Nagano City from the viewpoint of a new source of vitamin B_<12>. Pilot plant for the treatment of distillers' wastes is conducted in the amount of 0.9-1.8 tons per day at the Fermentation Institute, while 45 tons per day of wastes is treated at the Yoshinoya Factory. Determinations carried out on the samples from the both plants indicate that 30-87 μg/g (on dry basis) of vitamin B_<12> is contained in the centrifuged precipitates of effluents and that the high content of the vitamin in the precipitates seems to be attributed to bacteria capable of producing the vitamin.