On designing of full container ship with cell constructions, new peculiar problems concerning torsional strength and vibration of ship's hull have been brought out due to the necessity of large hatch openings for handling containers, which were not required for designing of ordinary ships so far built. In this connection, we have synthetically carried out theoretical and experimental investigations so as to clarify these problems in Mitsubishi Heavy Industry, Ltd. This report describes some results of our experimental studies on the strength at hatch corner induced by torsional deformation of hatch opening. In these studies, the following two experiments were carried out. (1) Experiments using three dimensional steel models made similar to actual structure. (2) Experiments using two dimensional photo-elastic models. And, the conclusions obtained are as follows. (1) The effects on the stress concentration of several types of hatch corner can be estimated by this investigation. (2) The hatch corner structure of the designed ship has sufficient strength for the torsional deformation of the ship.