Treatment of chemical mechanical polishing (CMP) wastewater is investigated. The CMP wastewater, as obtained from a large semiconductor manufacturer. was characterized by high suspended solids (SS) content, high Nephelometric turbidity unit (NTU), chemical oxygen demand (COD) concentration up to 500 mg/l, copper concentration over 100 mg/l and a milky color. This study was to explore the feasibility of treating the CMP wastewater by electrocoagulation with an aim of simultaneously lowering the wastewater turbidity, and copper and COD concentrations. Experiments were conducted to analyze the characteristics of the CMP wastewater and to evaluate the effects of electrocoagulation time, type of electrode pair and electrolyte dosage on the system performances. The fine suspended oxide particles were found to have an average size of 100nm with narrow particle size distribution between 68 and 120nm. The test results revealed that Al/Fe (anode/cathode) was a good electrode pair in terms of overall performances. Electrocoagulation with Al/Fe electrode pair was able to achieve 99% copper removal and 96.5% turbidity reduction in less than 100 min. The COD removal obtained in the treatment was better than 75%. with an effluent COD below 100 mg/l. The wastewater quality exceeded the direct discharge standard and the effluent can be considered for reuse. (C) 2003 Elsevier Science B.V. All rights reserved.