Reconstruction of the kinetics of relaxation processes induced in a medium by laser radiation is considered. Implementation of α-regularization algorithm of the ill-posed problem solution in optoacoustic (OA) diagnostics of liquids is discussed. The relationship between parameters of the diagnostic experimental set-up and the frequency band where relaxation spectra can be restored is established. The restoration algorithm is applied to analysis of OA-waveforms detected in aqueous solution near 4°C. It is shown that only broad-band detection could give necessary information for identification of particular relaxation mechanism in this case.