The possibility of electrical discharge machining (EDM) with ultralow discharge energy has been investigated. EDM using an RC discharge circuit was performed at low open-circuit voltages and a capacitance of approximately 30 pF. Workpieces were ultrasonically vibrated to remove debris and bubbles from the discharge gap, thus preventing short-circuiting. The machining proceeded at voltages lower than 15 V at a vibration amplitude of 0.4 μm. The maximum discharge energy per pulse is as small as approximately 3 nJ under these conditions. The volumetric electrode wear ratio can be 0.2% at voltages lower than 40 V, while it is normally more than 1% for EDM using an RC discharge circuit. Workpiece surfaces processed at voltages of 20 V or lower are smooth and free of observable discharge craters, and show no typical features of surfaces machined by EDM.