Melanoidins,　the　brown　late-stage　Maillard　reaction　products,　are　responsible　for　color　development　and　refractoriness　in　thermal　hydrolyzed　sludge　(THS),　causing　negative　effects　on　wastewater　treatment.　This　study　aimed　to　develop　a　methodology　for　the　identification,　isolation　and　preliminary　characterization　of　the　THS　melanoidins.　After　thermal　hydrolysis,　the　formation　of　melanoidins　were　confirmed　by　physicochemical　indicators　and　excitation-emission　matrix　fluorescence　analysis.　The　macroporous　resin　adsorption　method　was　adopted　to　successfully　extract　melanoidins　from　THS　with　high　recovery　and　selectivity.　The　main　chemical　components　of　the　extracted　melanoidins　were　carbohydrate　(23.1　%),　protein　(43.8　%)　and　phenol　(13.7　%),　and　the　C/N　was　4.5.　In　addition,　furans,　alcohols　and　sulfur-containing　volatile　substances　were　detected　by　pyrolysis-gas　chromatography–mass　spectrometry.　Fourier　transform　infrared　spectroscopy　determined　that　functional　groups　such　as　C[dbnd]O,　C–N,　N–H,　C-O-C,　amide　I　and　phenyl　were　present　in　the　structure　of　THS　melanoidins,　and　nuclear　magnetic　resonance　spectroscopy　indicated　the　formation　of　heterocyclic　macromolecular　structures.　Their　formation　pathways　were　speculated　to　involve　the　cross-linkage　of　low-molecular-weight　components　(e.g.　proteins,　Amadori　and　Schiff　base　compounds)　and　the　polymerization　of　heterocyclic　units　(e.g.　furans,　pyroles　and　pyrazines).　The　above　results　clarify　the　fundamental　characteristics　of　the　melanoidins　formed　during　sludge　thermal　hydrolysis　and　will　help　improve　subsequent　research　on　melanoidins　control.　©　2022　Elsevier　B.V.