Food additives, such as hypochlorous acid water, sodium metabisulfite, and sodium sulfite, strongly affect the chemical and biological properties of vitamin B 12 (cyanocobalamin) in aqueous solution. When cyanocobalamin (10 μmol/L) was treated with these compounds, hypochlorous acid water (an effective chlorine concentration of 30 ppm) rapidly reacted with cyanocobalamin. The maximum absorptions at 361 and 550 nm completely disappeared by 1 h, and vitamin B 12 activity was lost. There were no significant changes observed in the absorption spectra of cyanocobalamin for 0.01% (w/v) sodium metabisulfite; however, a small amount of the reaction product was formed within 48 h, which was subsequently identified as sulfitocobalamin through high-performance liquid chromatography. Similar results were shown for sodium sulfite. The effects of these food additives on the vitamin B 12 content of red shrimp and beef meats were determined, revealing no significant difference in vitamin B 12 content of shrimp and beef meats with or without the treatment even in hypochlorous acid water. The results suggest that these food additives could not react with food vitamin B 12 in food, as most of this vitamin present in food is its protein-bound form rather than the free form.