Abstract Information concerning the thickness of the damaged layer as well as the extent of the damage is very important for the minimization of damage caused by machining and the process to remove the damage. Thus a technique for evaluating the thickness of a heat-damaged layer on a ground surface, which has a metallurgical change, was investigated in this paper. The thickness as well as the extent of the damage was found to affect both the velocity and the reflection power of the surface acoustic wave. The relationship between the acoustic properties and the thickness was analysed on the basis of the theory of elasticity. The two-dimensional distribution of the thickness could be derived From the surface wave velocity utilizing the correlation when the dissipation of the surface wave was low in both the damaged layer and the bulk. However, the thickness was in fact evaluated in terms of the total reflection power when the attenuation of the acoustic wave was different from that in the bulk. The thickness estimated was confirmed to agree well with the results obtained by chemical etching.