The　textural　properties　and　surface　chemistry　of　phosphoric　acid-modified　biochars　(PABCs)　prepared　at　different　pyrolysis　temperatures　(500–700 °C)　were　studied　based　on　the　results　obtained　from　XRD,　SEM,　BET,　FT-IR,　Raman,　XPS　and　elements　analyses.　PABCs　prepared　at　higher temperatures　tended　to　possess　a　bigger　proportion　of　microporous　structure.　The　adsorption　capacity　and　initial　rate　of　PABCs　for　sulfadiazine (SDZ)　were　notably　improved　to　139.2 mg/g　and　9.66 mg/(g min)　as　calculated　from　the　Langmuir　model.　The　adsorption　equilibrium　time　was　only　one　quarter　of　that　without　modification.　The　H3PO4　modification　was　advantageous　to　produce　phosphate　and　break　functional　groups　to　form　disordered　carbon　structure　abundant　of　micropores.　The　enhancement　in　the　adsorption　of　SDZ　was　due　to　the　confinement　effect　of　hydrophobic　cavities　from　the　mircoporous　structure　and　the　π–π　electron–donor–acceptor　interaction.　Specially,　PABCs　exhibited　stable　adsorption　capacities　at　a　wide　pH　range　(3.0–9.0)　or　relatively　high　concentrations　of　coexisting　ions.　©　2022,　The　Author(s).