Abstract. In the present work we investigate the estimation of the thermal diffusivity with an inverse problem approach for photoacoustic spectroscopy (PAS). The direct problem is solved analytically using Rosencwaig-Gersho (RG) theory and the inverse problem is solved using the method of Levenberg-Marquardt. A sensitivity analysis is presented. We used real experimental data for the amplitude and phase-lag of the photoacoustic signal, acquired with a PAS experimental apparatus. A discussion is presented on the results obtained for the thermal diffusivity of a glass sample.