An experimental study was carried out to investigate the force in drilling of engineering ceramic with a brazed diamond tool. The drilling forces and protrusion heights of diamond grains were measured. The results showed that the variation of cutting forces, increasing with the cutting time, was divided into three phases for a drilled hole. For each phase, the variation of cutting forces was different. The drilling forces also increased with the numbers of drilled holes due to the wear of diamond grits. The distance values of the cutting force between the end of first phase and the end of second phase approximately kept constant.