The source analysis of AE due to the crack extension in ceramics is described. The vertical force released by the pencil lead fracture has been used as the artificial AE source. The transfer function of input/output signals is determined experimentally. Analysis is first carried out to investigate the phenomena of dips induced prior to the arrival of the surface stress emission. The amplitude of the dip depends on the length of the lead, which suggests that the creation of the dip might be caused by the stress pulse from the lead. It is shown that the AE source wave, D, associated with the crack extension in graphite corresponds well to an energy release rate, G. Results in vitrified grinding wheels with different grain diameters reveal the tendency of the AE source waveforms to coincide with each other irrespective of microstructures.