Initial deflections caused by welding have a considerable effect on the ultimate strength of welded plate structures. Therefore, it is important to know the magnitude and shape of initial deflections. Much research has been conducted on the initial welding distortions of steel structures. However, for aluminium alloys’ structures, the data on fabrication-related initial deflections are minimal. Therefore, in this paper, the initial deflections caused by welding are investigated in aluminium plates used for marine structures. Initial deflections of plating between stiffeners are measured for different panels of four aluminium vessels. Vessels were constructed by the metal inert gas (MIG) welding method. Statistical analysis of measured data is carried out for estimating the maximum value of the initial deflections of aluminium plating between stiffeners. The results of this paper can be applied for the ultimate strength calculations of aluminium marine structures.