Treatment of oily wastewater produced from post-treatment unit of refinery processes using flocculation and micro-filtration with zirconia membrane was studied in this paper. The results show that the oil content and COD value were decreased dramatically by flocculation, and the optimum flocculent is 35305 which is a derivative of polyacrylamide. The influence of flocculation conditions on flocculation results is also investigated by orthogonal experiments, and the optimum conditions are dosage of 70 mg/l, temperature of 40 degreesC, stirring time of 90 min and holding time of 90 min. After flocculation, the effluents were treated with micro-filtration using zirconia membrane. The results of filtration tests show that the membrane fouling decreased and the permeate flux and permeate quality increased with flocculation as pretreatment. The permeate obtained from flocculation and micro-filtration can meet the National Discharge Standard and the recommended operation conditions for pilot and industrial application are transmembrane pressure of 0.11 MPa, and cross-flow velocity of 2.56 m/s. (C) 2003 Elsevier Science B.V. All rights reserved.