This paper presents a study on acoustic emission (AE) in the bending fatigue process of spur gear teeth. Research was conducted on AE signals, AE cumulative event count, AE event count rate, frequency spectra of AE signals and crack length in the bending fatigue process of case-hardened and normalized spur gear teeth. The relationship between the AE parameters and the fatigue crack propagation, as well as the effects of the gear material and the case depth on the AE characteristics in the fatigue damaging process of the gear tooth, was determined. Basic data were obtained for the prediction of bending fatigue crack initiation of the gear tooth by means of the AE method.