Arsenic accumulation in Hijiki, Sargassum fusiforme (Harvey) Setchell, a member of the Phaeo-phyta Family, was determined throughout the whole plant by thermal neutron activation analysis. We collected Hijiki plants along a sea coast of Ise Bay, where Akamoku plants have also been harvested. The arsenic distri-bution in the Hijiki plant body was not uniform along the stalk like in Hijiki plants harvested at other districts and Akamoku plants of this district. Arsenic distribution in the genital organs of Hijiki showed high arsenic con-centrations on the wet weight basis in comparison with other tissues. (accepted. Oct. 25, 2008)