The performance and microbial community of a sequencing batch biofilm reactor (SBBR) treating synthetic mariculture wastewater were evaluated under long-term exposure to norfloxacin (NFX) due to the overuse of antibiotics during the mariculture. The COD and NH4+-N removals had no distinct change at 0-6 mg L-1 NFX and were inhibited at 6-35 mg L-1 NFX. The specific oxygen uptake rate (SOUR), specific ammonium oxidation rate (SAOR), specific nitrite oxidation rate (SNOR) and specific nitrate reduction rate (SNRR) of the biofilm kept a decreasing tendency with the increase of NFX concentration from 0 to 35 mg L-1. The presence of NFX promoted the microorganisms to secrete more extracellular polymeric substances (EPS) and affected the chemical compositions of EPS. The microbial richness and diversity showed some obvious variations at different NFX concentrations. The present results demonstrated that NFX inhibited the SBBR performance and should decrease the NFX dosage in the mariculture. (C) 2016 Elsevier Ltd. All rights reserved.