In electrical discharge machining (EDM), a process utilizing the removal phenomenon of electrical discharge in dielectric, the working fluid plays an important role affecting the material removal rate and the properties of the machined surface. In this paper the machining characteristics of Ti-6Al-4V were investigated with kerosene and distilled water as the dielectrics. The results show that the material removal rate is greater and the relative electrode wear ratio is lower, when machining in distilled water rather than in kerosene. By using X-ray diffraction, it is confirmed that carbide (TIC) and oxide (TiO) are formed on the workpiece surface when using kerosene and distilled water, respectively. The lower removal rate when machining Ti-6Al-4V ahoy in kerosene can be explained by both the formation of TiC, which has a higher melting temperature and therefore requires a larger discharge energy, and carbon deposition on the electrode, causing further retardation of the discharge process. A larger amount of debris and more micro cracks are also found when using distilled water as the dielectric. (C) 1999 Elsevier Science S.A. All rights reserved.