In　order　to　analyses　the　accumulating　behavior　of　nonylphenol　(NP)　in　aquatic　environment,　the　biodegradability　of　NP　isomers　in　the　wastewater　bio-treatment　process　was　studied　by　sequencing　batch　reactor　(SBR)　and　mass　spectrogram　interpretation.　The　results　show　that　the　residual　content　of　three　kinds　of　NP　isomers　was　markedly　higher　than　that　of　other　isomers　in　the　effluent　and　activated　sludge　of　SBR.　It　is　possible　for　three　isomers　to　accumulate　in　an　aquatic　environment.　The　isomers　have　comparatively　lower　biodegradability　than　other　isomers.　The　biodegradation　of　NP　isomers　in　wastewater　bio-treatment　process　is　associated　with　the　structural　difference　in　the　branches　of　nonyl.