•More than 80% of COD, NH4+-N and TP were removed under OFL pressure.•OFL promoted the secretion of EPS and changed the EPS chemical composition.•OFL decreased the diversity and richness of the microbial community in the reactor.•OFL affected the read numbers of the functional bacteria community in the reactor. An activated sludge sequencing batch reactor (SBR) was fed with synthetic wastewater containing ofloxacin (OFL) for 52days to study the overall performance of the SBR, the characteristics of extracellular polymeric substances (EPS) and the bacterial community shift. Removal efficiencies of chemical oxygen demand, ammonia nitrogen, phosphorus and OFL were maintained at 90%, 96%, 80% and 65%, respectively. The EPS contents increased with increasing OFL concentration because more EPS was secreted to protect cells from OFL damage. Moreover, the EPS compositions shifted. For denitrifying bacteria, the read number of Pseudomonas and Bacillus sharply decreased initially (p<0.05) and increased from Day 25 to Day 50, which agreed with the tendency of Nitrosomonadaceae (ammonia oxidizer), while Paracoccus significantly decreased (p<0.05). The read number of Rhodocyclaceae, a phosphorus-accumulating bacterium, increased. Other functional microbes such as Nitrospirales (nitrite oxidizer) and Planctomyces (anammox) sharply decreased under OFL pressure (p<0.05).