In order to investigate the transverse strength of bulk carriers, experimental tests have beer made on six newly built ships, including 16, 000 DWT class to 55, 000 DWT class bulk carriers. The tests have been carried out under such loading condition of filling sea water into their top side tanks, and the measurements have been made on the hold frame stresses as well as on the vertical and the horizontal deflections of upper deck construction. Based on the results of these, analytical formula has been deduced to calculate the hold frame strength, which can illustrate fairly well the mechanical behavior of bulk cargo carrier constructions, and the frame stresses have been evaluated for various loading conditions. The general conclusions obtained from this investigation are as follows. (1) Degree of the end fixty of hold frames is usually lowered by the deformations of hopper or top side tank constructions in the plane of their transverse cross section. In this analysis, an equivalent span of the hold frames is introduced to calculate the frame stresses instead of directly considering the effect of their plane deformations. (2) The load carried by web frames and ordinary frames is almost proportional to their values of the moment of inertia, and thus the bending moment in extraordinary large sized web frames becomes comparatively large one. (3) The effect of load acting on the bottom structures on the magnitude of frame stresses is usually significant. (4) Fairly high stresses might take place in hold frames under certain loading conditions, e. g. in an empty hold under fully loaded draft condition.