In ship structures, diminution and deterioration of structural members are serious problem. And the diminution of structural members have an effect on the deterioration of structural performance of ship hull. Hence it is necessary to investigate the relation between the diminution of structural members and the deterioration of structural performance of ship hull. This paper describes followings. (1) Statistical characters of annual corrosion rate of each member. (2) Deteriorating rate of section modulus of hull due to diminution of structural members. (3) Buckling strength of stiffened panel considering the effect of structural diminution and deterioration.