A curved-hole machining method by EDM using an electrode consisting of a metal ball suspended with a lead copper foil from the spindle head of an electro-discharge machine has been proposed and the fundamental machining characteristics has been discussed. This paper discusses the effects of the diameter and mass of the metal ball on electrical discharge machining characteristics. The use of a 5.5-mm-diameter ball electrode may provide stable machining performance under a wide range of electric conditions. On the other hand, with decreasing ball diameter and mass, the stably machinable conditions are limited to lower discharge current and higher servo voltage. A smaller diameter hole can be machined by using a 3.0-mm-diameter ball under the optimum conditions. Additionally, a curved hole with small diameter is successfully machined by varying the tilt angles of the workpiece during the process.