Recently, AFM with suitable tips is being used for nano fabrication/nano machining purposes. In this paper Acoustic emission(AE) was introduced to monitor the nano machining of brittle materials (silicons) using AFM. In the experiments, AE responses were sampled, as the tip load was linearly increased (ramped load), to investigate the machining characteristics. By analysing 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 the nano machining. The critical depth of cut value for the transition is evaluated and discussed.