For investigating the effect of heating and cooling process assuming fire of steel bridges on characteristics of welded joints of structural steel members, a series of experiments were carried out. The heating under transformation point did not affect the joint performance regardless of cooling process. The heating over transformation point caused the softening or the hardening according to cooling rate. The degree of them was larger in the base metal rather than in the weld metal because the amount of carbon in the base metal was more than that in the weld metal. Furthermore, the change of microstructure of base metal made by TMC process was more sensitive compared with that of weld metal.