Investigations were made on the precipitating reagents for vitamin B_<12>. The results indicated that mercuric ion was no less effective for precipitating dicyanocobalamin than other cations reported such as those of Cu, Co, Ni, Zn, Ag. Further experiments on the precipitating behavior of oxides of the metals described above showed that HgO and Ag_2O had a strong affinity not only to dicyanocobalamin but also to cyanocobalamin, while Fe_2O_3,Co_2O_3,Ni_2O_3,CuO and ZnO had little or no effects on vitamin B_<12> and its dicyanide. The effective metallic oxides tested could be used as a kind of adsorbents for vitamin B_<12>, since they are very difficult soluble in water. Vitamin B_<12> could be recovered very effectively from these precipitates by eluting with aqueous (NH_4)_2HPO_4 solution. Precipitation procedure based on these results would be used for purifying vitamin B_<12> from activated sludge or anaerobic fermentation products of distillers' wastes.