It has been reported that ionic liquids (ILs) are commonly toxic in nature, and thus the removal of ILs in various environmental systems would be of great significance. In this work, an ultrasonic irradiation and zero-valent iron activated carbon (ZVI/AC) micro-electrolysis system was applied to degradation of 1-butyl-3-methylimidazolium chloride ([C(4)mim]Cl) residues in water. The experimental conditions were optimized, and the degradation processes were investigated by using UV, HPLC and GC-MS techniques. It was found that more than 95% of [C(4)mim]Cl could be degraded in aqueous solution and 81% of [C-4-mim]Cl could be mineralized within 110 min, and the degradation could be described by a pseudo-first-order kinetics. The presence of hydroxyl radical scavenger can greatly reduce the reaction rate but could not prevent degradation of [C(4)mim]Cl. GC-MS analyses demonstrated that this degradation led to the formation of 1-butyl-3-methyl-2,4,5-trioxoimidazolidine, 1-butyl-3-methylurea and N-butylformamide. On the basis of these intermediates, degradation pathway was also suggested. These results indicate that ZVI/AC micro-electrolysis with ultrasonic irradiation degradation could serve as an efficient treatment technology for removing [C(4)mim]Cl from wastewater. (C) 2012 Elsevier B.V. All rights reserved.