Seaweeds　consumption　is　one　of　main　internal　exposure　sources　of　arsenic　for　human.　However,　the　absence　of　representative　bio-availabilities　of　arsenic　species　makes　the　accurate　assessment　of　arsenic　health　risk　originating　from　seaweeds　consumption　impossible.　Herein,　the　arsenic　species　in　various　seaweeds　collected　from　Fujian　of　China　were　investigated,　and　the　bio-accessibilities/bio-availabilities　of　arsenic　species　existing　in　seaweeds　were　evaluated　in　vitro　and　in　vivo　.　Results　revealed　that　in　vitro　bio-availabilities　of　arsenic　species　presenting　in　seaweeds,　which　obtained　with　Caco-2　cells,　were　lower　than　those　of　pure　arsenic　standards,　and　varied　with　order　of　inorganic　arsenic　(iAs)　＞　dimethylarsinic　acid　(DMA)　approximate　to　arsenobetaine　(AsB)　＞　arsenosugars.　During　gastrointestinal　digestion　of　mice,　As(　5　+　)was　partly　methylated　into　monomethylarsonic　acid　(MMA)　and　DMA,　which　makes　the　in　vivo　bioavailability　of　iAs　(-31.8　%)　obtained　with　mouse　metabolic　experiment　is　much　higher　than　its　in　vitro　bio-availability　(-10.3　%).　The　in　vivo　bio-availabilities　of　DMA　and　total　arsenic　(tAs)　are　similar　to　their　in　vitro　bio-availabilities.　As　the　dominant　arsenic　species　in　most　seaweeds,　arsenosugars　have　an　-0.0　%　of　in　vivo　bioavailability　and　only　a　-3.7　%　of　in　vitro　bioavailability.　The　simulated　calculation　of　target　hazard　quotient　(THQ)　and　target　cancer　risk　(TR)　revealed　that　the　arsenic　risk　originating　from　seaweeds　was　greatly　degraded　by　taking　into　consideration　of　arsenic　species　and　bio-availabilities,　and　all　seaweeds　collected　from　Fujian　are　safety　for　consumption.　The　simulated　calculation　also　revealed　that　arsenic　risk　of　seaweeds　can　be　also　more　accurately　assessed　based　on　tAs　together　with　bioavailability,　which　provides　a　simple　but　accurate　and　protective　method　for　the　risk　assessment　of　arsenic　originating　from　seaweeds.　Our　work　provides　the　possible　representative　bio-availabilities　of　arsenic　species　presenting　in　seaweeds　for　accurately　assessing　arsenic　risk　of　seaweeds,　and　novel　insights　into　the　bio-availabilities　of　arsenic　in　animal.