An attempt has been made to evaluate the grade from the analysis of AE signals detecting small amounts of energy release caused by the fracture of the local area of the wheel surface. Present report mainly describes; (1) the characteristics of AE wave propagation in the wheel, (2) quantitative relationship between AE counts and the amount of fracture by using the Okoshi's grade testing machine, and (3) strain rate dependence of AE, respectively. Ringdown counting is selected by taking into account of both intervals of AE events and ringing time. In order to compare each data quantitatively, sensitivity is adjusted such that the counts of artificial AE wave obtained by rupture of lead (HB) indicate same value. Specimens tested are 15 different kinds of vitrified wheels. The results are as follows : (1) As frequency of AE waves, the frequency component more than 350 kHz should decrement during wave propagation in the wheel and that AE counts are independent of natural frequency. (2) AE counts should have one to one correspondence to the amount of fracture.