Soil　arsenic　(As)　fractionation　and　its　bioaccessibility　are　two　important　factors　in　human　health　risk　assessment.　However,　data　related　to　the　impact　of　As　minerals　on　the　bioaccessibility　with　human　gut　microbiota　involvement　are　scarce.　In　this　study,　speciation　analysis　was　determined　using　HPLC-ICP-MS　and　XANES　after　incubation　with　colon　microbiota　from　human　origin,　in　combination　with　sequential　extraction.　Significant　increase　of　colon　As　bioaccessibility　was　contributed　primarily　from　As　associated　with　amorphous　and　crystalline　Fe/Al　(hydr)oxides.　We　found　a　high　degree　of　transformation　at　higher　bioaccessibility　(ave.　40　%　of　total　As),　which　was　predominantly　present　as　liquid-phase　As.　In　contrast,　As　transformation　occurred　mainly　in　the　solid　phase　at　lower　bioaccessibility　(　©　2020　Elsevier　B.V.