In this study, the tensile and compressive behaviours of corroded steel-stiffened plates were experimentally investigated, and the effects of pitting- and grooving-corrosion damage on the residual strengths of corroded stiffened plates were evaluated. Two series of tests were conducted for this study: one involved tensile test on specimens having natural corrosions and artificially machined corrosions, and the other involved compression tests on damaged stiffened plates having artificially machined corrosions. Naturally corroded tensile specimens were obtained from an aged ship. The profiles of the naturally corroded tensile specimens were measured using a three-dimensional (3-D) scanner and a dial thickness gauge. Tensile tests were conducted on nine naturally corroded and fifteen artificially machined specimens. Compression tests were performed on seven stiffened plates having artificially machined corrosion damage. Pitting- and grooving-corrosions were considered in the compression tests. Before these tests, the initial shape imperfections of the stiffened plate models were measured using a 3-D scanning machine. Test results including load-displacement relationship and the ultimate strength under compressive loads were analysed. Finite element (FE) modelling and analyses were performed in this study using commercial software CATIA and ABAQUS. The outputs of numerical analyses were compared with the corresponding test results, and a reasonable agreement between the test results and numerical predictions is shown.