The adsorption behaviors of about 20 kinds of commercial active carbon for vitamin B_<12> and impurities contained in the aqueous extract obtained from the activated sludge were investigated from the viewpoint of an industrial purification of the vitamin. According to the results obtained with "Strong-Shirasagi" from Takeda Pharmaceutical Co.Ltd., seemed to be most suitable for the purpose, in view of the adsorption capacity, the price of active carbon, the easiness of filtration and the elution behavior with 50% acetone.