[en] The effects of aging on the tensile properties and fracture behaviors of U-0.75%Ti and U-2.0%Mo are discussed. Both alloys can be quenched from the γ-phase field to produce supersaturated martensitic variants of the α-phase. Subsequent aging at temperatures below approximately 425⁰C causes substantial increases in strength. Overaging occurs at temperatures above approximately 425⁰C. In U-0.75%Ti desirable combinations of strength and ductility are obtained only in underaged conditions. The decrease in ductility and toughness which occurs during aging is due to a transition from fracture across the martensite plates to fracture along the martensite plate boundaries. The martensitic structure in U-2.0%Mo exhibits inherently poor ductility and toughness. Substantial ductility is obtained in this alloy only after the equilibrium phases are restored by severe overaging. (Auth.)