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The tensile property and surface composition of U-2%Nb alloy after long storage at different humidity and in underwater environment have been investigated. The results show that the samples stored in 10% humidity environment for 5 years have almost the same tensile property as un-stored samples in the same batch, and are of ductile fracture character. The samples stored at 100% humidity or in underwater environment exhibit a little reduction of tensile strength and remarkable drop of plastic property, and present distinct brittle fracture character. Raman analysis indicates that the primary composition of the surface of the sample in dry environment is UO2, while the sample at 100% humidity or in underwater environment is U3O8 and other UO2+x oxides.