FEM analysis is carried out to clarify the strength of double hull Afra-Max tanker which has neither center line longitudinal tight bulkhead nor swash bulkhead. And following results are obtained. The depth of double bottom is most important item on the design viewpoint of double hull Afra-Max tanker, and the deformations at bottom and side shell of double hull Afra-Max tanker are larger than those of ordinary single hull tanker, The bottom girder and side stringer are effective to reduce the deformation of double bottom and side shell, especially to reduce the relative deformation between the bulkhead and the adjacent transverse web. And the side stringer already attached to double hull tanker is very useful to reduce the stress in transverse web. The shearing stress is dominant at the point where large von Mises equivalent stress is calculated in transverse web, which can be reduced by using thicker plate.