In wire electrochemical micromachining, insoluble products are still generated in spite of the use of acidic electrolyte and adhere onto the wire cathode. In this work, the compositions of the adhered products and their influences on the electrochemical characteristics of the wire cathode were studied. The XRD results suggest that the insoluble products are mainly composed of gamma-Fe2O3 and alpha-FeOOH and that reduction of Fe ions occurs on the wire cathode to form metallic Fe (alpha-Fe). In addition, the electrochemical impedance spectroscopy measurement results indicate that the electrochemical characteristics of the wire cathode are significantly affected by the insoluble products. These insoluble products together with the deposited iron on the wire pose negative effects on the machining results. Finally, qualitative models for the cathodic reactions are proposed. (C) 2018 Elsevier Ltd. All rights reserved.