Fatigue tests on ship hull structures have been conducted by R. Weck and J. J. W. Nibbering and also in Japan by Mitsubishi Heavy Industries, Ltd. and other shipbuilders. On the basis of the results of these tests, this paper deals with a tentative plan of a fatigue design diagram centering on consideration of fatigue crack initiation life. Structural members under consideration are transverse strength members with joints, longitudinal strength members with openings and longitudinals with scallops. In calculating damage (D), the hot spot stress is used which is obtained by multiplying nominal stress by given stress concentration ratio K_t in cracked part of each structural member and stress increase ratio K_e due to decrease in effective width of face bars. The diagram shows the lower limit of the relation between the hot spot stress and crack initiation life N_c . By using the diagram, frequency distribution of external force, and Miner's law, the possibility of fatigue failure of each structural member can be examined by whether damage (D) is greater than 1.0 or not. The author has verified the appropriateness of the design diagram by comparing it with analysis results of fatigue failures in actual ship and the diagram has been compared with the fatigue test results of basic welded joints of simple shapes and the fatigue test results of smooth, simple shape specimens by constant strain amplitude.