This paper presents the results of theoretical and experimental investigations on the torsional strength of large container ships having large hatch openings. Especially the effect of the double hull structure on the strength was studied. The feature of the method of calculation is that the ship structure is treated as a beam shell having multi-cell structure and the effect of the double hull is directly developed. Further, the influence of cross decks between hatch openings is studied. A series of experiments was carried out and it was confirmed that calculated results obtained through this method are in good agreement with experimental results. Also, the double hull structure and cross decks were found to increase the torsional strength of ships.