An atomic force microscope (AFM) with suitable tips has been used for nano fabrication/nanometric machining purposes. In this paper, acoustic emission (AE) was introduced to monitor the nanometric machining of a brittle material (silicon) using AFM. In the experiments, AE responses were sampled, as the tip load was linearly increased (ramped load), to investigate machining characteristics during continuous movement. By analyzing the experimental results, it can be concluded that measured AE energy is sensitive to changes in the mechanism of material removal including the ductile-brittle transition during nanometric machining. The critical depth of cut value for the transition is evaluated and discussed.