The main objective of this reported research is to develop an efficient treatment method for pharmaceutical wastewater by combining ozonation and biological treatment. The antibiotic ciprofloxacin (CIP) was used to prepare synthetic pharmaceutical wastewater. The effect of ozonation on wastewater was assessed by antibacterial activity and biodegradability index. The inhibitory effect of raw and ozone pre-treated wastewater on biomass oxygen uptake was examined and compared with that of biodegradable non-inhibitory compound (sodium acetate). The raw and ozone pre-treated wastewater were used in batch bioreactor experiments. It was found that the pre-treatment by ozone increased the biodegradability index from 0.13 to 0.32 and reduced the antibacterial activity of wastewater. The activated sludge inhibition test showed that a total of 77% and 46% inhibition in raw wastewater and ozone pre-treated wastewater, respectively. This result were corroborated by the substrate removal kinetic models, that the ozone-treated wastewater has more biodegradable compounds through the enhanced biomass growth in the batch bioreactor. The combined ozonation and biological treatment removed 82.5% of Chemical Oxygen Demand (COD), whereas 38% of COD was removed in biological treatment alone. The two-step treatment (ozonation and biological) process was applied to real pharmaceutical wastewater and the treatment efficiency was evaluated. © 2020 Elsevier B.V.