This paper presents the shear stress distribution of the web and the ultimate shear strength for the plate girder with cross-sectional defects caused by local corrosion. Loading tests and nonlinear FEM analyses are conducted on the locally corroded plate girder cut from the railway bridge, which has been used for about 100 years. From results, it is concluded that the shear stress distribution can be obtained based on the beam theory, and that the ultimate shear strength can be evaluated from the buckling strength formula of shear plate without corrosion by substituting the representative web thickness into the formula, in which the representative plate thickness can be decided by the average thickness and the standard deviation in local corrosion area.