Abstract Recently, an electrical discharge machining (EDM) method of insulating ceramics was proposed by the authors. This paper describes the arbitrary shape machining method of Si 3 N 4 insulating ceramics by WEDM. In the WEDM of thick workpieces of Si 3 N 4 insulating ceramics, wire breakages occurred frequently. To avoid the breakage conditions, a new assisting electrode material was used. Using this method, a thin ceramics sheet was hollowed out of Si 3 N 4 ceramics without breakages. In the machining of thin sheets, a warping phenomenon is observed to occur towards the end of the product owing to thermal residual stress. The amount of warp is dependent on, and can be reduced considering, the machining path. Furthermore, an axisymmetric products can be machined by this method with a rotating workpiece system.