In this report authors carried out structural study on a wide-beam tanker with DW 400, 000 T. L / B ratio of this vessel is five, whereas that of conventional tankers is about six. Main items of the study are as followings : - (1) Selection of structural system Comparative study for probable three structural systems are carried out from strengthwise and constructionwise view-points. Finally, structural system with center line bulkhead is selected. (2) Longitudinal strength Wave bending moment and shearing force on this type of vessel are relatively smaller than those on conventional tankers. (3) Transverse strength Transverse strength for structure selected under (1) is checked by using 3-D frame analysis method. (4) Shear strength of hull girder in way of engine room At the fore end of engine room center line bulkhaed terminates and in view of such structural discontinuity shear strength is checked by replacing the structure with a beam element model. As a result it proved that the shear strength of this part is enough. (5) Reaction force from supporting blocks imposed to hull during construction In view of fairly big canti-lever type stern construction, reaction force from supporting blocks are feared to become a big amount and calculation of this reaction force is carried out. In result the force is found to be below allowable limit but to secure sufficient allowance, development of suitable method to support the weight of stern construction is desired. Through these studies authors reached the conclusion that the main problems pertaining to the structural design of this type of vessel have almost been solved and construction of this vessel is possible.