Using Lamb waves, the influence of the welding quality of thin steel sheets on the physical and mechanical properties of electrical steel has been studied. It is shown that Lamb waves excited in the zero symmetric mode are an effective source of information about the state of the material both in the welded joint of plates and in the region of the base metal not affected by thermal effects. Markers of quality of welded joints are determined. It has been established that the most informative parameters are the phase velocity of the Lamb wave and its amplitude. On the basis of velocity measurements, a macroscopic anisotropy of the acoustic properties of the material was found. It is assumed that the origin of this anisotropy is due to residual stresses that arise in the technological process of processing steel sheets. The results obtained are of interest for specialized quality control of butt welds in thin steel sheets.