Electrical discharge machining (EDM) technologies is widely used to manufacture complex shaped dies, molds and critical parts in conductive materials. With the help of assisting electrode (AE), EDM process can also be used to machine non-conductive ceramics. This paper evaluates the mechanical properties of 3 high performance non-conductive ceramics (ZrO2, Si3N4 and SiC) that have been machined with the EDM process using AE. Optimized set of EDM parameters obtained from previous studies are used for the machining purpose. Mechanical properties such as Vickers hardness (HV 0.3), the surface roughness (Sq) and the flexural strength are presented. These mechanical properties of the machined and the non-machined samples are compared. The EDM process causes decrease in Vickers hardness, increase in surface roughness and decrease in flexural strength. The surface roughness has a significant effect on the flexural strength of the material. The flexural strength was measured according to the DIN EN 843 specification.