To　assess　the　condition　of　phthalic　acid　esters　(PAEs)　held　up　in　the　environment,　and　predict　its　biodegradability　and　provide　basic　data　for　sludge　treatment　and　disposal,　the　aerobic　biodegradation　characteristics　of　six　PAEs　in　the　sewage　sludge　was　investigated,　and　a　model　of　the　quantitative　relationship　between　aerobic　biodegradability　and　chemical　structure　(QSBR)　was　established.　The　results　show　that　the　degradation　of　six　PAEs　in　the　sludge　conforms　to　the　first-order　reaction　kinetic　equations.　Their　biodegradability　decreases　with　the　increase　of　the　carbon　numbers　of　alkyl　chains,　and　the　steric　factor　represented　by　molecular　connection　indexes　is　an　important　parameter　affecting　the　aerobic　biodegradability　of　the　tested　PAEs　in　the　sludge.