This paper describes summarized results of the appraisal on measured corrosion data of hull structure which are obtained through periodical surveys, the corrosion test of specimens of various weld joint, the fatigue test and the stress analysis of corroded specimens. To grasp the conditions of corrosion and the strength is indispensable for the integrity of hull structure through ship's life. Statistical analysis of pitting corrosion on bottom plate of oil tankers is carried out with good results. It is also found that tank cleaning has considerable effect on the progress of pitting corrosion. Data of plate thickness on lower part of side frames of bulk carriers is appraised by two parameters namely initiation life and progress rate of corrosion wastage. The results show that the progress rate of corrosion wastage is larger than conventional numerals. Corrosion test of weld joint specimens is carried out under the cycles of sea water and the air. Grooving corrosion has initiated at weld toe of butt joints as a result of the test. The cause of grooving corrosion is presumed due to difference of corrosion potential between HAZ and base metal/weld metal of the specimen. Tensile fatigue test and stress analysis of corroded specimens are carried out. The results are examined as to the relation of fatigue strength and stress concentration factor. It is confirmed that in the case of butt joint stress concentration factor has increased by corrosion and then fatigue strength is reduced. On the other hand, in the case of cruciform joint the factor has nearly unchanged and then the fatigue strength is almost not reduced.