Electircal Discharge Machinable (EDM) Si-based ceramics such as silicon nitride and silicon carbide were fabricated with adding the conductive particales up to 60 vol%. theire sinterbility, microstructure, mechanical, and electrical properties were characterized as function of the content of the conductive particles. The Si-based ceramics with the content of 40 vol% appear to be optimally machinable for EDM with relatively good mechanical and electrical properties.