It　is　very　important　to　consider　the　bio-accessibilities　and　concentrations　of　each　arsenic　species,　not　total　arsenic,　in　seafood　in　order　to　accurately　assess　internal　exposure　level　and　health　risk　of　arsenic　from　seafood.　Herein,　the　concentrations　and　in　vitro　bio-accessibilities　of　each　arsenic　species　in　various　fishes　and　shellfishes/　shrimps　were　extensively　investigated.　Experimental　results　showed　that　arsenic　species　and　contents　in　shellfishes/fishes　remarkably　varied　with　the　difference　of　fish/shellfish　species　or　individuals　and　sampling　area,　and　arsenobetaine　(AsB)　is　dominant　arsenic　species　for　fishes　and　shellfishes/shrimps.　Different　arsenic　species　in　the　same　fish/shellfish　have　quite　different　bio-accessibilities,　and　the　bio-accessibilities　of　each　arsenic　species　also　varied　with　fish/shellfish　species　or　individuals.　As3+　in　fishes/shellfishes　was　partly　oxidized　to　form　As5+　during　gastrointestinal　digestion,　and　thus　it　is　more　reasonable　and　practicable　to　evaluate　the　bio-accessibilities　of　inorganic　arsenic　(iAs,　total　As3+　and　As5+),　not　individual　As3+　and　As5+.　Fishes　and　shellfishes/shrimps　have　similar　bio-accessibilities　of　iAs,　AsB　and　total　arsenic,　whereas　have　different　bio-accessibilities　of　MMA　(monomethylarsonic　acid),　DMA　(dimethylarsinic　acid),　and　two　un-identified　arsenic　(Ui-As1　and　Ui-As2).　The　results　of　this　study　provided　a　valuable　knowledge　for　accurately　assessing　the　health　risk　of　arsenic　in　seafood.