Seafood　consumption　is　the　major　source　of　total　Hg　(tHg)　and　methyl　mercury　(MeHg)　for　humans.　Lack　of　broad-representative　bio-accessibility　of　mercury　species　makes　accurate　assessment　on　health　risk　of　seafood＇s　mercury　impossible.　Herein,　the　concentrations　and　in　vitro　bio-accessibilities　of　mercury　species　in　93　seafood　samples　with　71　different　species　were　extensively　investigated.　Results　indicated　that　all　shellfish　and　fish　samples,　and　most　seaweed　samples　contained　both　Hg2+　and　MeHg,　while　some　seaweed　samples　contained　only　Hg2+.　The　concentrations　of　mercury　species　varied　depending　on　the　differences　in　species/individuals　of　seafood　and　sampling　regions.　MeHg　in　seafood　can　be　partly　de-methylated　into　Hg2+　during　gastrointestinal　digestion,　which　reduced　the　toxicity　of　mercury　in　seafood.　The　mean　demethylation　rate　of　MeHg　varied　as　follows:　seaweeds　(⁓62.1　%)　＞　shellfishes/shrimps　(⁓19.7　%)　＞　fishes　(⁓9.2　%).　The　mean　bio-accessibility　of　Hg2+　and　tHg　varied　as　follows:　seaweeds　(⁓97.7　%　and　⁓90.1　%)　＞　shellfishes/shrimps　(⁓65.1　%　and　⁓67.9　%)　≈　fishes　(⁓65.1　%　and　⁓66.7　%),　while　that　of　MeHg　varied　as　follows:　fishes　(⁓57.7　%)　＞　shellfishes/shrimps　(50.8　%)　＞　seaweeds　(⁓11.6　%).　The　simulated　calculation　of　target　hazard　quotient　(THQ)　revealed　that　the　health　risk　of　seafood＇s　mercury　may　be　accurately　assessed　using　tHg,　not　mercury　species,　even　without　considering　bio-accessibility.　This　offers　a　simple　but　protective　approach　for　assessing　the　health　risk　of　seafood＇s　mercury.　Results　of　this　study　provide　the　potential　broad-representative　bio-accessibilities　of　mercury　species　existing　in　various　kinds　of　seafood　and　novel　insights　for　scientifically　assessing　the　health　risk　of　seafood＇s　mercury　and　revising　the　mercury　limitation　in　seafood.　©　2024　Elsevier　B.V.