It was found that ductility of steel plate under statical bending was affected by shape of specimen, especially ratio of width to thickness of plate by our experimental investigation and a new method for statical bending test of steel plate was proposed¹⁾. Generally, stiffend panels in ship structure has large aspect ratio and many cracks were found in plane strain state of panels under bending loads. Therfore, in this report fatigue tests of steel plates of various width to thickness ratio were carried out by Schenk type fatigue machine and the effect of shape of the plates on the strength was discussed. From these test results, the follwing conclusions were obtained. 1) The constraint to deformation of transvers section of plate increases with increase of width to thickness ratio. Strain distribution approaches to pure plane strain state and fatigue life decreased with increase of the ratio. 2) Ductility of plate under statical bending is affected mainly by strain conditions on surface of the plate and secondarily by the strain gradient in cross section of the plate. 3) Fatigue strength of plate is much more affected by the ratio than in case of statical test and therfore shape of the speciemen should be decided in considaration of the above results.