Recently,　the　use　of　biochar　for　wastewater　treatment　has　become　a　central　focus　in　environmental　remediation　studies.　In　this　research,　a　simple　and　economical　one-pot　hydrothermal　strategy　was　developed　for　the　synthesis　of　iron-modified　sludge-derived　hydrothermal　biochar　(ISHB).　The　obtained　optimum　ISHB　possesses　abundant　hydroxy,　carboxyl　and　aromatic　ring　surface　functional　groups　as　well　as　relative　high　surface　area　and　small　particle　size　which　contribute　to　the　adsorption　of　the　enhanced　contaminants.　The　structure-activity　relationship　and　the　adsorption　behavior　between　the　ISHB　and　doxycycline　(DOX)　were　explored.　The　loaded　iron　improved　the　adsorption　capacity　of　ISHB　from　51.65　to　78.93　mg　g(-1)　at　20　degrees　C　with　an　initial　DOX　concentration　of　60　mg　L-1.　As　Cu(II)　exists　in　the　DOX　solution,　the　adsorption　of　DOX　is　inhibited　to　50.06　mg　g(-1)　due　to　the　site　competition　between　DOX　and　Cu(II).　Nevertheless,　the　adsorption　of　Cu(II)　is　promoted,　which　can　be　explained　by　the　complexation　between　DOX　and　Cu(II).