Abstract: Wire electro discharge machining (WEDM) has become one of the most popular processes for producing precise geometries in hard materials, such as those used in the tooling industry. With the demands on the minimization of surface roughness, decrease of the producible geometric dimensions and improvement of the machining accuracy, Micro-Wire-EDM with a wire diameter of 80μm-250 μm has been a key technology for micro-machining. This work deals with the effect of the input parameter i.e thickness of the job on output parameters such as discharge current, cutting speed, spark gap/over cut, metal removal rate and surface roughness value of high carbon high chromium steel (HC-HCr), a die steel cut by wire-electrical discharge machining (WEDM). To obtain a precise workpiece with good quality, the parameters to be set on the machine are optimized experimentally. The output criteria can be estimated for a given thickness of the workpiece using the mathematical correlations developed.