The welded connectors in the plate girder, that is, the cover plate, the transverse stiffener and the gusset plate were selected as studying objects. One series of these were made of SS41 steel, and the other series were made of SWS50 steel. The direct fatigue test were carried out. From the results, the S-N curves were drawn, and the fatigue properties were examined to be compared with each other. The results of these studies were following. It was shown that the fatigue strength of modeling specimens was much lower than that of the base metal, in sequence most in the cover plate, next in the transverse stiffener and next in the gusset plate. It was shown that in all modeling specimens the fatigue strength of the high strength steels was much lower than that of the low strength steels under the high stress range. It was shown that in the cover plate the fatigue strength of the high strength steels was lower even while the low stress range. It was shown that the fatigue strength of steels containing the high percentage carbon was much lower.