Despite　rice　consumption,　rice　bran　as　a　byproduct　of　rice　milling　contains　higher　arsenic　(As).　The　present　study　evaluated　the　metabolic　potency　of　in　vitro　cultured　human　colon　microbiota　toward　As　from　five　rice　bran　products　with　0.471-1.491　mg　of　As/kg.　Arsenic　bioaccessibility　ranged　from　52.8　to　78.8%　in　the　gastric　phase,　and　a　1.2-fold　increase　(66.0-95.8%)　was　observed　upon　the　small　intestinal　phase.　Subsequently,　a　significant　decline　of　As　bioaccessibility　(11.3-63.6%)　and　a　high　methylation　percentage　of　18.5-79.8%　were　found　in　the　colon　phase.　The　predominant　As　species　in　the　solid　phase　was　always　As(V)　(49.6-63.4%),　and　As-thiolate　complexes　increased　by　10%　at　the　end　of　colon　incubation.　Human　gut　microbiota　could　induce　As　bioaccessibility　lowering　and　As　transformation　in　rice　bran,　which　illustrated　the　importance　of　food-bound　As　metabolism　in　the　human　body.　This　will　result　in　a　better　understanding　of　health　implications　associated　with　As　exposures.　Copyright　©　2019　American　Chemical　Society.