Experiments on the corrosion fatigue of welded steel joints in air and seawater, and in seawater with cathodic protection, yielded bata for linear regression to obtain fatigue-life curves(?S-Nf). The laws of corroion fatigue in welded joints of test steel are discussed with referrence to those of A587 and A131 steels there. In the expriments above, the fatigue damage occurring at all welded joints around the weld bead resulted in the cracking and fracture there. The fatigue life of the speciments in seawater was longer than that in seawater, almost reaching the length of the fatigue life in air.