Spot welds are widely used to join plate structures such as an automotive body and the vibration characteristics of the whole structure are affected by the spot welded joints. For the spot welded structure, the actual spot welding location is often misaligned from the design specific location. In this paper, we investigate the effect of welding location variability on the vibration characteristics of plate structures based on Fuzzy finite element method (FFEM) with Monte Carlo simulation. From the membership functions of the natural frequencies from the FFEM and the histograms of the natural frequencies from the interval analysis in the FFEM, we examine the modes that are strongly affected by welding location variability and the locations that strongly affect the vibration characteristics. As an example structure, the structure consisting of hat section steel plates joined together by 20 spot welds at the flanges is used.