In　this　study,　we　investigated　the　application　risks　of　oxalic　acid,　a　classic　mobilizing　agent,　by　examining　arsenic　(As)　fractionation/　speciation,　leachability,　and　oral　bioavailability/　bioaccessibility.　Advanced　methodologies,　including　the　toxicity　characteristic　leaching　procedure　and　both　in　vivo　and　in　vitro　tests,　were　employed.　The　results　revealed　that　oxalic　acid　significantly　enhanced　the　mobility　of　arsenic　in　terms　of　fractionation.　The　proportion　of　labile　arsenic　(As)　fractions,　comprising　the　water-soluble　and　exchangeable　fractions,　increased　by　1.　85　times　following　mobilization.　Concurrently,　the　combined　proportion　of　amorphous　and　crystalline　As　was　significantly　reduced.　This　led　to　a　marked　increase　in　the　ecological　risk　associated　with　soil　As,　with　leachability　rising　by　an　average　of　3.　59　times.　Notably,　in　both　in　vivo　and　in　vitro　tests,　oxalic　acid　was　found　to　reduce　the　health　risks　posed　by　arsenic.　In　the　mouse　model,　oxalic　acid　significantly　decreased　the　relative　bioavailability　of　arsenic　(As).　Using　the　PBET　-　SHIME　model,　we　observed　that　oxalic　acid　notably　reduced　As　bioavailability　during　the　colon　phase.　Additionally,　oxalic　acid　inhibited　the　reduction　of　bioaccessible　As(Ⅴ)　and　promoted　the　methylation　of　bioaccessible　As(III),　which　is　associated　with　higher　toxicity　in　colon　fluid,　thereby　further　mitigating　health　risks.　The　observed　phenomena　can　primarily　be　attributed　to　the　release　of　excessive　metal　components　from　the　soil　due　to　oxalic　acid　and　the　metabolism　of　oxalic　acid　by　gut　microbiota.　Notably,　consistent　trends　were　observed　across　all　soil　samples　following　the　application　of　oxalic　acid,　highlighting　the　generalizability　of　its　effects　on　soil　arsenic　(As).　In　summary,　as　a　typical　low-molecular-weight　organic　acid,　oxalic　acid　is　highly　recommended　for　the　mobilization　and　remediation　of　As-contaminated　soils.　This　study　provides　valuable　scientific　information　for　selecting　mobilizing　agents　for　As-contaminated　soils　and　serves　as　a　reference　for　risk　control　at　remediation　sites.　©　2025　Science　China　Press.　All　rights　reserved.