The structural changes of sintered WC-(10-20)mass%Co and WC compacts along the machining surface obtained by electric discharge machining using fine wire were studied. The three sorts of carbides, W₂C, β-WC_1-x (B1 type) and WC, were generally detected along the surface, with no cobalt and η phases in both compacts. The appearance of different phases of W₂C and β-WC_1-x was assumed to result in the fact that the high temperature phase (β-WC_1-x ) crystallized in non-equilibrium state in the course of rapid cooling of molten WC produced during electric discharge machining, and that the eutectoid reaction of β-WC_1-x into W₂C Plus WC took place incompletely. Some microstructural changes due to the machining were examined.