In order to evaluate the fatigue strength of the marine propellers of aluminium bronze castings, corrosion fatigue tests under synthetic sea water were carried out by using a great number of specimens taken out from three actual propellers different from both mass and size, while the examination of defect distribution was made on them. Defects were examined in detailes all over the propellers with penetrant or visual method. The fatigue test results were statistically settled considering scatter of fatigue lives. Then the correlation between the fatigue strength and the defect distributions was discussed by introducing statistics of extremes on the basis of the weakest link theory. As the results, it was concluded that the fatigue strength is dependent upon the defect distribution, that is, the failure probability relates to the existence probability of maximum defect size at the concerned region. Finally, the reasonable fatigue strength diagram for design was proposed taking into account of survey periods, etc.