When asakusanori was incubated in artificial seawater, it released a significant amount of vitamin B12. The rate of release was very high at the beginning of incubation and steeply decreased. Four-fifths of the released B12 was a macromolecule-bound form and the rest was free form, of which some were taken up by the asakusanori tissue. Asakusanori took up the free form B12 from the incubation medium by concentration- and temperature-dependent processes. The amount of uptake increased with the time of incubation and did not attain a plateau after 4 h. The capacity was retained even after storage in frozen state for 11 months.