Quinclorac　is　an　herbicide　widely　used　in　rice　production,　and　its　residue　in　water　and　soil　poses　significant　threats　to　aquatic　organisms　and　subsequent　crops.　We　herein　isolated　a　group　of　aptamers　with　high　binding　affinity　to　quinclorac　using　library-immobilized　SELEX.　Notably,　one　of　these　aptamers　(Apt.Q1)　demonstrated　excellent　specificity　and　affinity　to　quinclorac,　with　dissociation　constant　(Kd)　of　8.7　+/-　2.4　mu　M　and　no　interference　from　structurally　similar　pesticides.　Molecular　dynamics　simulations　identified　the　G-rich　loop　in　Apt.Q1　as　the　potential　binding　domain,　and　circular　dichroism　analysis　revealed　the　conformational　transition　from　hairpin　to　G-triplex　structure　upon　quinclorac　interaction.　Moreover,　a　one-step,　label-free　colorimetric　biosensor　was　developed　based　on　quinclorac-mediated　displacement　of　Cy7　dye　and　Apt.Q1　for　detecting　quinclorac　within　1　min　with　a　detection　limit　of　237　nM　and　RSD　＜　5%.　Assessment　of　quinclorac　residues　in　soil　and　river　water　using　the　biosensor　demonstrated　recoveries　of　89-92%.　The　study　not　only　provided　a　promising　bioreceptor　for　developing　various　quinclorac　biosensors　but　also　provided　a　cost-effective　tool　for　rapidly　screening　quinclorac　in　environment.　Specifically,　the　investigation　of　the　recognition　mechanism　between　Apt.　Q1　and　quinclorac　lays　a　theoretical　foundation　for　designing　more　sensitive　and　reliable　sensing　platforms　for　quinclorac　detection.