Abstract: Photoacoustic measurement techniques can be used to determine thermal properties on and below the sample's surface, thus subsurface thermal inhomogeneities, such as continuous profiles of thermal parameters, become to be measurable by photoacoustic methods. In this paper, the study is focused on the quantitative characterization of material modifications in subsurface layers of laser-hardened Al alloy samples. The variation of surface temperature is measured by PA technique. Then a new numerical algorithm, carried out by employing the pulsed spectrum technique and the regularization method, is used to reconstruct thermal conductivity depth profiles. The experiment results are compared with those of Vickers microhardness depth profiles obtained by destructive method. It is demonstrated that there exists a close anticorrelation between microstructure depending hardness and local thermal conductivity. The presented results show the experiment and the algorithm is very effective for microstructure depth profile reconstruction by nondestructive method.