Bones absorb a considerable amount of uranium under the reducing environment due to the decomposition of organic matters soon after their burying. The daughter nuclides of uranium, such as thorium-230 (half-life of 75 200 y) and protactinium-231 (half-life of 32 800 y) are absent soon after the bone burying, and their quantity grows with time. The age of ancient bones can therefore be determined by the measurements of these daughter nuclide activities in comparison with their parent activities, uranium-234 and uranium-235. These parent and daughter nuclides emit gamma-rays of specific energies, so they can be determined by the high-resolution gamma-ray spectrometry. The ages of ancient human bones can therefore be determined by the non-destructive gamma-ray spectrometry. Many bones are dated in this way, for example, Tautavel man (about 450,000 y BP), Kafzeh man (94,000 ± 10,000 y BP) and Minatogawa man (19,200 ±1,800 y BP).