There have thus far been no reports on the drilling of microholes in cemented tungsten carbide by cutting. Such drilling was therefore attempted using micro-diamond end-mill-type tools fabricated by EDM. The assistance of ultrasonic oscillation was employed to reduce cutting force and thus to prevent tool breakage. At an ultrasonic oscillation half amplitude of 0.2 μm, the drilling of microholes up to 15 μm in depth was possible at a feed speed of 0.05 μm/s using a 20-μm-diameter tool.