The optimum condition selection of rotary dressing operations using Hall and AE sensor is presented. The acquired current signals from a hall sensor were studied as one of the method to obtain the optimum condition of dressing and the correlations between dressing condition and AE signals were also evaluated with the root mean square (RMS). Dressing operation was performed to investigate the effects of depth of cut, rotating speed and coolant. In order to verify the optimum condition of dressing, AE and hall sensor signals were compared in RMS with the surface micrograph of grinding wheel. This verification experiment demonstrates the effective dressing condition selection for centerless grinding.