Nuclear fuel reprocessing plant releases several kinds of radioactive nuclides, mainly 3H and 129I, into the oceans. Radio iodine causes thyroid dose. Iodine accumulates in several marine species such as wakame and abalone, which are food materials. Therefore, an analysis of iodine behavior in the marine environment is important to assess the impact of 129I. Iodine in seawater exists mainly in two chemical forms: iodide (I−) and iodate (IO3−). Their environmental behaviors are different. Thus, understanding these behaviors is important to assess the environmental behavior of total iodine. In this study, iodate and iodide transfer between seawater and abalone (Haliotis discus hannai) with 125I tracer was observed.