There is a limitation to estimate vitamin $B_{12}$ intake due to a lack of data on vitamin $B_{12}$ content in many Korean foods. In this study, vitamin $B_{12}$ content was determined in some seaweeds, fish, and shellfish and their product that are consumed in Korea using a modified microbioassay with Lactobacillus delbruecki ATCC 7830. Dried laver and dried seasoned and toasted laver contained very high levels of vitamin $B_{12}$ (66.8 and $55.2-71.3;{mu}g$/100 g, respectively. Sea lettuce and seaweed fulvescene also contained high vitamin $B_{12}$ content of 5.47-9.41 and $6.46-7.20;{mu}g$/100 g, respectively, whereas sea mustard and sea tangle contained low levels of vitamin $B_{12}$; vitamin $B_{12}$ was not detected in seaweed fusifome. Pacific saury, trout, sea-bass, or squid contained 12.01, 2.00, 0.49 and $2.33;{mu}g$ vitamin $B_{12}$/100 g, respectively. Ochellatus octopus, and naked sand lance contained 0.72-1.43 and $3.68;{mu}g$ vitamin $B_{12}$/100 g, respectively. Dried Alaska pollack con-tained $0.19-2.64;{mu}g$ vitamin $B_{12}$/100 g. Shellfish such as little neck clam and small ark shellfish contained high levels of vitamin $B_{12}$ of $30.5-40.5;{mu}g$/100 g, and mussel and abalone contained 17.71 and $7.82;{mu}g$/100 g, respectively. Of unique Korean traditional fermented seafood products, salt-fermented products of squid ($2.91;{mu}g$/100 g), clams ($34.31;{mu}g$/100 g), Ala-ska pollack roe ($9.98-12.02;{mu}g$/100 g), hairtail guts ($4.58;{mu}g$/100 g) or small shrimp ($0.58-1.55;{mu}g$/100 g), and fish sauce from anchovies ($1.52-1.78;{mu}g$/100 mL), sand eel ($0.22-0.24;{mu}g$/100 mL) or small shrimp ($0.19-0.78;{mu}g$/100 mL) were analyzed. A few commercial brands of flying fish roe ($0.73-1.73;{mu}g$/100 g), canned tuna ($0.40;{mu}g$/100 g), and fried fish paste ($0.25-0.69;{mu}g$/100 g) were also analyzed. In conclusion, vitamin $B_{12}$ content in these foods, chosen considering the Korean food culture, should contribute to improve the present vitamin $B_{12}$ food database. It may be helpful to estimate vitamin $B_{12}$ intake more correctly than before, and provide additional information for dietary education related to vitamin $B_{12}$ and meal management.