The 1789 discovery of uranium in the mineral pitchblende is credited to Martin Heinrich Klaproth, who named the new element after the planet Uranus.
V naravi se nahaja kot uran-238 (99.2739–99.2752%), uran-235 (0.7198–0.7202%), in zelo majhna količina uranium-234 (0.0050–0.0059%).