Developing　safe　and　efficient　diclofenac　sodium　(DS)　removal　technology　has　become　a　critical　issue.　This　study　synthesized　the　fish-scale　biochar　by　co-pyrolysis　of　fish　scale　and　phosphoric　acid　(H3PO4).　In　addition　to　increasing　the　specific　surface　area　and　pore　volume　of　fish-scale　biochar,　H3PO4　assisted　in　the　formation　of　Graphitic　N　and　sp2　C,　as　well　as　reacting　with　CO　groups　to　form　a　significant　number　of　phosphorus-containing　groups.　All　these　functional　groups　could　act　as　major　active　sites　for　DS　adsorption.　Adsorption　data　could　well　fit　pseudo-second-order　and　Langmuir　models.　The　maximum　adsorption　capacity　of　FSB600-15　for　DS　was　967.1　mg　g−1,　which　was　much　better　than　that　reported　in　the　literature.　Under　the　synergistic　effect　of　various　mechanisms　(pore-filling　effect,　electrostatic　attraction,　H-bonding,　π-π,　and　n-π　electron　donor-acceptor　interactions),　the　DS　ultra-efficient　adsorption　on　FSB600-15　was　realized.　Meanwhile,　the　DS　adsorption　by　FSB600-15　was　an　endothermic,　spontaneous,　and　entropy-increasing　process.　Furthermore,　the　DS　adsorption　capacity　was　more　than　426.5　mg　g−1　in　the　actual　water,　which　was　sufficient　for　practical　applications.　©　2023　Elsevier　Ltd