Increase of tanker size may be accompanied with the problem that hull deformation will affect alignment of shafting and turbined gear in various conditions. We investigated deformation of hull structure by FEM calculation and measurement of 270, 000 & 410, 000 DWT turbine tankers. The results of FEM calculation agree rather well with the measurement of actual ship (270, 000 DWT tanker). In this paper, we would report some results as reference for structural design. The summary is as follows. (1) Shear rigidity of hull girder affects the response of double bottom deflection. Therefore, 3-dimensional calculation is useful for checking the bouble bottom design. (2) In way of narrower breadth of double bottom, vertical deflection is much affected by bending moment carried from pressure on side shell than by vertical pressure from bottom shell. (3) Variation of loading weight in engine room, and L. O. temperature seem to give some effects on hull deformation and alignment of shafting. (4) Reverse deflection in (2) due to side pressure works good effection on shafting as a cancellation factor of upward deflection of double bottom due to bottom pressure.