The　prevalent　presence　of　fluoroquinolone　antibiotics　in　aquatic　environments　has　attracted　considerable　attention　because　of　their　harmful　effects　on　humans　and　the　ecological　environment.　Magnesium　hydroxide　nanocrystals　were　found　to　act　as　a　simple　and　effective　adsorbent　to　remove　low-concentration　ciprofloxacin　(CIP)　in　aqueous　solution.　The　as-prepared　Mg(OH)(2)　nanocrystals　exhibited　excellent　CIP　adsorption　performance　and　high　selectivity　toward　CIP　molecules　compared　with　other　antibiotics　or　aromatics,　e.g.,　norfloxacin　(NOR)　and　eosin　B　(EB).　The　adsorbent　showed　pH-dependent　adsorption,　indicating　that　the　adsorption　process　is　probably　dominated　by　an　electrostatic　interaction　mechanism.　In　addition,　structural　analysis　of　the　adsorbent　indicated　that　coordination　and　hydrogen　bonding　between　CIP　and　Mg(OH)(2)　nanocrystal　might　also　be　involved　in　the　adsorption　process.　Moreover,　the　adsorbent　could　be　easily　recovered　by　pyrolysis　and　hydration　without　significant　reduction　of　adsorption　capacity.　The　superior　adsorption　behavior　of　Mg(OH)(2)　nanocrystal　indicates　that　it　may　serve　as　a　potential　adsorbent　material　candidate　for　the　selective　removal　of　CIP　from　aquatic　environments.　(c)　2019　The　Research　Center　for　Eco-Environmental　Sciences,　Chinese　Academy　of　Sciences.　Published　by　Elsevier　B.V.