Marine organisms contain arsenic at various concentrations, and so human consumption of seafood products results in arsenic intake. Therefore, identification and quantification of all arsenic compounds present in seafood products are important from the viewpoint of food hygiene, because the toxicity of arsenic strongly depends on its chemical form. Hence, determination of total arsenic concentration and speciation analysis of arsenic compounds in seafood products have been extensively performed. This review covers the large number of arsenic compounds identified in seafood products, and summarizes recent findings on their biological effects and metabolism in humans and experimental animals.