Selective　detection　of　organic　arsenic　from　waste　water　of　livestock　farms　is　important,　but　challenging.　As　newly　developed　porous　materials,　metal-organic　frameworks　(MOFs)　are　promising　for　sensing　of　organic　pollutants.　In　this　work,　two　stable　isostructural　Al-MOFs,　Al(CTTA)　(BUT-18)　and　Al(CETA)　(BUT-19),　were　designed　and　synthesized　for　the　selective　detection　of　two　representative　organic　arsenic　compounds,　roxarsone　(ROX)　and　nitarsone　(NIT),　in　water,　and　they　present　excellent　performance.　To　the　best　of　our　knowledge,　this　is　the　first　exploration　for　the　application　of　MOFs　in　the　detection/sensing　of　organic　arsenic.　The　quenching　efficiencies　of　ROX　and　NIT　on　BUT-18　and　-19　are　all　beyond　98%.　The　limits　of　detection　(LOD)　of　BUT-18　toward　ROX　and　NIT　are　estimated　to　be　15.7　and　32.2　ppb,　and　those　of　BUT-19　are　13.5　and　13.3　ppb,　respectively.　This　work　indicates　that　MOFs　are　favorable　materials　for　the　selective　detection　of　organic　arsenic,　being　potentially　useful　in　monitoring　drug　residues　in　waste　waters.