Tungsten carbide - Cobalt (WC-Co) reinforced metal matrix composites are most commonly used as tool and die materials. The machining of WC- Co metal matrix composites is usually done by wire electric discharge machining. However during WEDM of WC-Co samples possibility of defects and electrolyzation is high. Also coating of Cu-Zn tool electrode on machined surface and void space takes place, thereby affecting material integrity. Analyzing the microstructures can remarkably reveal the identification, location, extent and criticality of the defects. In this study WC-Co metal matrix composite was wire electric discharge machined with two critical parameters, pulse on time and delay time. The machined samples were analyzed using micrographs, scanning electron microscope, EDAX and the results tabulated. It was found, that lower pulse-on time and medium pulse-off time leads to less rapid quenching and subsequent improvement in surface finish, less craters, voids. This prevents potential sites for defect and weakening of material by filling with cu-zinc particles for unbounded tungsten particle.