This paper deals with the effect of input parameters of Powder Mixed Electric Discharge Machining (PMEDM) process on the surface roughness when processing cylindrical shaped parts. In this work, the workpiece material is 90CrSi alloy tool steel and the nanopowder is silicon carbide. Also, five input parameters including the pulse on time, the pulse off time, the powder concentration, the current and the server voltage were selected to investigate their influence on the surface roughness. Taguchi method and ANOVA analysis were used and the effect of input parameters on the surface roughness was presented. Moreover, optimum input parameters for minimum surface roughness was suggested.