This paper presents the results of a study on optimizing Electrical discharge machining (EDM) when machining cylindrical parts made of 90CrSi tool steel to achieve the minimum surface roughness (SR). To do that, an experiment was performed. The Taguchi method in Minitab 19 software was used to design the experiment and analyze its results. The effects of the input process parameters, including the pulse on time, the pulse off time, the servo current, and the servo voltage on the surface roughness were investigated. Furthermore, optimal EDM parameters for minimal SR was proposed.