To circumvent the high cost of micro electro-discharge machining (MEDM) with superfine wire, the authors modified a conventional electro-discharge machine (EDM) by fitting a rotating disk as the electrode (RDE). Locating the electrode below the workpiece in the modified RDE-EDM, the debris removal rate was greatly improved. Further, by an improved fixture design to stabilize electrode vibration during machining and by a revised circuit designation to reduce the discharge current, micro slit machining was made feasible in practical application. A 42 mu m-wide micro slit with a depth of 1.02 mm was fabricated successfully on a Ti-6Al-4V workpiece by using 25 mu m thickness copper as the material of the rotating disk electrode and kerosene as the dielectric fluid. The effects of polarity, discharge current, pulse duration and rotational speed on the material removal rate (MRR), the electrode wear rate (EWR), the expansion of slit, the surface profile and the recast layer of micro slit machining are reported and discussed. (C) 1999 Elsevier Science S.A. All rights reserved.