Microcystins　(MCs),　which　are　produced　by　eruptive　cyanobacteria,　seriously　threaten　the　health　of　humans　for　their　poisonousness.　Herein,　a　facile　strategy　was　introduced　to　synthesize　the　magnetic　γ-cyclodextrin　polymer　(Fe3O4@PDA@γ-CDP)　composite　and　set　it　as　a　novel　adsorbent　with　excellent　properties　for　the　magnetic　solid-phase　extraction　(MSPE)　of　MCs.　The　prepared　Fe3O4@PDA@γ-CDP　microspheres　exhibit　good　aqueous　dispersibility　and　highly　affinity　for　MCs,　thus　contribute　to　an　excellent　extraction　performance　for　trace　MCs　in　water　samples.　Combined　with　HPLC–MS/MS,　a　handy,　sensitive　and　efficient　method　was　developed　for　detection　of　MCs　in　water　samples,　which　shows　good　linearity　(R2　≥　0.9992)　in　the　range　of　1.0–1000　pg　mL−1,　low　limits　of　detection　(0.8–2.0　pg　mL−1,　S/N　=　3),　satisfactory　repeatability　with　the　relative　standard　deviations　(RSDs)　lower　than　6.2%　(n　=　5).　At　last,　the　proposed　method　was　successfully　applied　for　the　extraction　and　detection　of　MCs　in　fresh　water　and　sea　water　samples,　which　provides　great　potential　of　trace-level　MCs　determination　in　lake　and　sea　water.　©　2018　Elsevier　B.V.