Fenton reaction with zerovalent iron (ZVI) and Fe2+ ions was studied to treat pharmaceutical wastewaters (PhWW) including antibiotics and non-biodegradable organics. Incremental biodegradability was assessed by monitoring biochemical oxygen demand (BOD) changes during Fenton reaction. Original undiluted wastewater samples were used as collected from the pharmaceutical factory. Experiments were carried out to obtain optimal conditions for Fenton reaction under different H2O2 and ion salts (ZVI and Fe2+) concentrations. The optimal ratio and dosage of H2O2/ZVI were 5 and 25/5 g/L (mass basis), respectively. Also, the optimal ratio and dosage of H2O2/Fe2+ ions were 5 and 35/7 g/L (mass basis), respectively. Under optimized conditions, the chemical oxygen demand (COD) removal efficiency by ZVI was 23% better than the treatment with Fe2+ ion. The reaction time was 45 min for ZVI and shorter than 60 min for Fe2+ ion. The COD and total organic carbon (TOC) were decreased, but BOD was increased under the optimal conditions of H2O2/ZVI = 25/5 g/L, because organic compounds were converted into biodegradable intermediates in the early steps of the reaction. The BOD/TOC ratio was increased, but reverse-wise, the COD/TOC was decreased because of generated intermediates. The biodegradability was increased about 9.8 times (BOD/TOC basis), after treatment with ZVI. The combination of chemical and biological processes seems an interesting combination for treating PhWW.