The influence of the quality of welding thin steel sheets on the physical and mechanical properties of electric steel has been studied using Lamb waves. 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 the plates and in the zone of base metal not affected by thermal influences. Markers of the quality of welded joints are determined. It is established that the most informative parameters are the phase velocity of a Lamb wave and its amplitude. Based on velocity measurements, macroscopic anisotropy of the acoustic properties of the material is found. It is assumed that the origin of this anisotropy is due to residual stresses arising in the technological process of processing steel sheets. The results obtained are of interest for specialized quality control of butt joints in thin steel sheets.