In the EDM process an electrical discharge occurs between an anode (graphite or copper) and a cathode (material to be machined) in a dielectric medium. Developments in EDM technologies have opened a new path towards high-precision, more productive machining of high alloyed, high hardness and high strength steels . Wire EDM offers an efficient and cost effective alternative to traditional machining in tool and component manufacturing . EDM machining removes electrically conductive material with rapid and repetitive spark emissions using a dielectric fluid. As a result, the surface of the raw material is subject to erosion. The quality of the machined surface depends to a large extent on the parameters of the machining technology . In the testing experiments, wire EDM machining was performed on two tool steel grades using different machining parameters. After each machining step, hardness and roughness tests were performed on the surface of the workpiece. Scanning electron microscopy was performed on the machined surface. The tests confirmed that the surface quality of the tools is significantly influenced by the parameters set during the EDM. The change of parameters was achieved by performing multiple cutting threads. By using the multiple cutting thread, tools with favourable surface roughness have been produced for tool steels with a high hardness of quenched and tempered heat treatment state.