The resistance spot welding is one of the main methods used to join thin-walled metal parts, while a number of factors adversely affect the process and thus the quality of the connections made. This article presents the study results of the possibility of applying modal analysis in the quality examination of welded parts by detecting the missing weld. It was aimed to determine this kind welding process imperfections influence on modal shapes and frequencies by the study of the dynamic properties of welded elements in the frequency domain. The research included real and numerical tests. The proposed testing method for spot welded constructions is a scientific novelty in the world, but the investigation results indicated, that the modal analysis may find application in detecting welding defects such as the lack of the welds. To assess the quality of the numerical models, the results obtained in the simulation and experimental test results were compared. The analysis involved the first five modes. The mode shapes in relation to the first five modal frequencies identified using the FEM analyses and the experimental tests was consistent with respect to element distortion. The differences indicate the satisfactory conformity of the numerical simulation results with the experimental test results. The article fundamentally demonstrates the applicability of the above-mentioned method to analyse the performance of all welds at once.