Fenton process was employed to pretreat the acrylic fiber manufacturing wastewater. The operation conditions were as follows: H2O2 and ferrous dosages were 100-800 mg/L; pH value was 1-7; reaction time was 0.5-4.0 h. In terms of COD removal and biodegradability improvement, the optimal conditions were as follows: ferrous content was 300 mg/L; hydrogen peroxide was 500 mg/L; pH value was 3.0; reaction time was 2 h. With these conditions, the overall COD removal and effluent B/C could arrive at 65.5% and 0.529 respectively. The biodegradability of the acrylic fiber manufacturing wastewater was increased by 429%. It was unnecessary to achieve complete mineralization of the organic compounds into carbon dioxide and water. Partial oxidation of intermediate compounds could minimize the consumption of chemical reagents and result in substantial reduction of COD and toxicity. The further biological treatment was favored by acquiring degradable low molecular weight components. (C) 2011 Elsevier B.V. All rights reserved.